A huge earthquake killed more than 2,600 people and injured thousands more on Monday in Turkiye and northwest Syria, flattening apartment blocks and heaping more destruction on Syrian cities already devastated by years of war.

The magnitude 7.8 quake brought down whole apartment blocks in Turkish cities and piled more devastation on millions of Syrians displaced by years of war.

The worst tremor to strike Turkey this century, it came before sunrise in harsh weather and was followed in the early afternoon by another large quake of magnitude 7.7.

“It was like the apocalypse,” said Abdul Salam al-Mahmoud, a Syrian in the northern town of Atareb. “It's bitterly cold and there's heavy rain, and people need saving.”

The second quake was big enough to bring down more buildings and, like the first, was felt across the region, endangering rescuers struggling to pull casualties from the rubble.

In Diyarbakir in southeast Turkiye , a woman speaking next to the wreckage of the seven-storey block where she lived said: “We were shaken like a cradle. There were nine of us at home. Two sons of mine are still in the rubble, I'm waiting for them.”

She was nursing a broken arm and had injuries to her face.

In Turkiye, the death toll stood at 1,651, Health Minister Fahrettin Koca said, and 11,119 people were recorded as injured. At least 968 people were killed in Syria, according to figures from the Damascus government and rescue workers in the northwestern region controlled by insurgents.

Poor internet connections and damaged roads between some of the worst-hit cities in Turkey's south, homes to millions of people, hindered efforts to assess and address the impact.

Temperatures in some areas were expected to fall to near freezing overnight, worsening conditions for people trapped under rubble or left homeless. Rain was falling on Monday after snowstorms swept the country at the weekend.

It is already the highest death toll from an earthquake in Turkey since 1999, when a tremor of similar magnitude devastated the heavily populated eastern Marmara Sea region near Istanbul, killing more than 17,000.

Turkish President Tayyip Erdogan, who is preparing for a tough election in May, called it a historic disaster and the worst earthquake to hit Turkiye since 1939, but said authorities were doing all they could.

“Everyone is putting their heart and soul into efforts although the winter season, cold weather and the earthquake happening during the night makes things more difficult,” he said.

Turkish state broadcaster TRT showed a building collapse in the southern province of Adana after the second quake. It was not immediately clear if it was evacuated.

In Syria, already wrecked by more than 11 years of civil war, the health ministry said 461 people had been killed and more than 1,326 injured. In the Syrian rebel-held northwest, a United Nations spokesperson said 255 people had died.

The Norwegian Refugee Council said the earthquake would only add to the suffering of millions of Syrians already enduring a humanitarian crisis due to the civil war.

In the Turkish city of Diyarbakir, Reuters journalists saw dozens of rescue workers searching through a mound of debris, all that was left of a big building, and hauling off bits of wreckage as they looked for survivors.

Occasionally they raised their hands and called for quiet, listening for sounds of life.

Men carried a girl wrapped in blankets from a collapsed building in the city. In Izmir, drone footage showed rescue workers stood atop a hill of rubble where a building once stood, working to lift slabs of masonry.

Footage circulated on Twitter showed two neighbouring buildings collapsing one after the other in Syria's Aleppo, filling the street with billowing dust.

Two residents of the city, which has been heavily damaged in the war, said the buildings had fallen in the hours after the quake, which was also felt in Cyprus and Lebanon

'Like the apocalypse'

In the Syrian rebel-held town of Jandaris in Aleppo province, a mound of concrete, steel rods and bundles of clothes lay where a multi-storey building once stood.

“There were 12 families under there. Not a single one came out. Not one,” said a thin young man, his eyes wide open in shock and his hand bandaged.

Raed Fares of the Syrian White Helmets, a rescue service in the rebel-held territory known for pulling people from the ruins of buildings destroyed by air strikes, said they were in “a race against time to save the lives of those under the rubble”.

Abdul Salam al Mahmoud, a Syrian in the town of Atareb, said it felt “like the apocalypse”. Syrian state television showed footage of rescue teams searching for survivors in heavy rain and sleet.

President Bashar al-Assad held an emergency cabinet meeting to review the damage and discuss the next steps, his office said.

People in Damascus and in the Lebanese cities of Beirut and Tripoli ran into the street and took to their cars to get away from their buildings in fear of collapses, witnesses said.

Footage on broadcaster CNNTurk showed the historic Gaziantep Castle was severely damaged.

In the Turkish city of Malatya, a rescue worker crawled into a collapsed building, trying to identify a survivor trapped under the wreckage, in footage released by Turkiye's Disaster and Emergency Management Authority (AFAD).

“What colour are you wearing? Are you wearing pink? Please take care of yourself for the moment, I cannot see anything else,” the rescue worker could be heard saying.

Worst quake since 1999

Erdogan said 45 countries had offered to help with the search and rescue efforts.

The United States was “profoundly concerned” about the quake and was monitoring events closely, White House national security adviser Jake Sullivan said on Twitter. “We stand ready to provide any and all needed assistance,” he said.

The US Geological Survey said the quake struck at a depth of 17.9 kilometres. It reported a series of earthquakes, one of 6.7 magnitude.

The region straddles seismic fault lines.

"The combination of large magnitude and shallow depth made this earthquake extremely destructive,” Mohammad Kashani, Associate Professor of Structural and Earthquake Engineering at the University of Southampton, said.

It was Turkiye's most severe quake since 1999, when one of similar magnitude devastated Izmit and the heavily populated eastern Marmara Sea region near Istanbul, killing more than 17,000.

Tremors were felt in the Turkish capital of Ankara, 460km northwest of the epicentre, and in Cyprus, where police reported no damage.

Pakistan sends doctors, paramedics to aid rescue efforts

In separate tweets on Monday, Prime Minister Shehbaz Sharif extended condolences and sympathies to the governments of Syria and Turkiye.

Later in the day, the premier spoke to the Turkish president on the phone and expressed deep grief over the loss of life and property.

“The people of Pakistan are with brotherly Turkiye and its people. Pakistan will extend its maximum support to the Turkish government and people to help them cope with the destruction,” he said.

"Natural calamities and climate change know no boundaries, region, or ethnicity," he remarked. The prime minister prayed to Allah Almighty for the departed souls and for the recovery of the injured.

Erdogan thanked PM Shehbaz for the condolatory call and for offering support, saying that he valued the sentiments of the prime minister as well as the Pakistani people.

Later, the premier announced that "teams comprising doctors, paramedics, and rescue workers" were being sent to Turkiye. "A plane carrying medicines and other essential relief goods is also being dispatched soon," he added.

Separately, Foreign Minister Bilawal Bhutto Zardari said he had spoken to his Turkish counterpart Mevlut Cavusoglu "in solidarity and to offer condolences". He added he had "offered assistance and support in any way" the country could.

"Search and rescue teams with equipment and medical supplies will leave as soon as possible," he added.

The Foreign Office said in a statement that the government and people of Pakistan were saddened to learn that a severe earthquake hit parts of Southern Türkiye earlier today, resulting in the loss of precious lives and extensive damage to property.

"The people of Pakistan stand in complete solidarity with our Turkish brethren in this hour of grief. We extend our deepest condolences to the bereaved families and pray for early recovery of those injured," it said.

The statement added that Pakistan stood ready to extend all possible support in the relief effort. "We are confident that the resilient Turkish nation will overcome this natural calamity with characteristic grit and determination."

In a subsequent statement issued later in the evening, the FO reiterated Pakistan's support to Turkiye, adding that the news of the quake was received by the people with "deep sorrow and anguish".

It added that, upon the premier's instructions, the National Disaster Management Authority was "mobilising all available resources including winterised tents, blankets and other critical life-saving supplies".

The FO highlighted "urban search and rescue teams trained to operate in disaster-hit areas" were being dispatched with their equipment and medicines.

"Our mission in Ankara remains in constant touch with the relevant Turkish authorities to identify any additional requirement for the earthquake-affected areas," it stated.

Pakistan also assured Turkiye it will continue to work with it in the "post-disaster rehabilitation and reconstruction phases" after the immediate relief effort.

The FO also said that Pakistan was ready to extend all possible support to Syria. "The government and the people of Pakistan are extremely saddened and shocked at the two successive earthquakes that hit Syria causing widespread devastation in the brotherly country," the FO statement said.

"Pakistan expresses solidarity with our Syrian brothers and sisters in this hour of grief and stands ready to extend all possible support in the relief efforts," it added.

Additional input from Naveed Siddiqui, APP