At least 276 people have been killed and 300 injured by a massive truck bomb that tore through a busy shopping district of Mogadishu, the government said on Monday, making it the “deadliest attack ever” to hit war-torn Somalia.

The figure was a huge jump from an initial police estimate of 20 dead in the hours after the deadly explosion ripped through the Somali capital on Saturday, causing scenes of carnage and widespread devastation.

“Somalia Federal government confirmed that 276 people were killed in the blast... and 300 others wounded people were admitted at the different hospitals in Mogadishu,” the country's ministry of information said.

“There is still national rescue operation,” ongoing the ministry said in a statement, adding that there would be “national mourning and prayers for the victims” in the coming days.

Police official Ibrahim Mohamed told AFP that many of the victims were “burned beyond recognition” in what he described as “the deadliest attack ever.”

Rescuers worked through the night to try to pull bodies from the rubble after the truck bomb exploded outside of the Safari Hotel on a busy road junction, levelling buildings and leaving many vehicles in flames.

“This is the most painful incident I can remember,” the deputy speaker of the Somali Senate Abshir Ahmed said in a Facebook post after visiting the Medina hospital where many of the victims had been taken.

There has been no immediate claim of responsibility, but the Shabab, a militant group aligned with Al Qaeda, has carried out dozens of suicide bombings in its bid to overthrow Somalia's internationally-backed government.

Saturday's blast was universally condemned, including by the United States, Britain, Canada, France, Turkey and the African Union.

Turkish President Recep Tayyip Erdogan's spokesman Ibrahim Kalin said Ankara was sending planes “with medical supplies”, adding that the wounded would be flown to Turkey and treated there.

The country is a leading donor and investor in Somalia.

'Stand united'

Mogadishu's mayor Tabid Abdi Mohamed also visited those wounded in the blast and said the horror of the attack was “unspeakable”.

“There is no tragedy worse than when someone comes to the dead body of their relative and cannot recognise them.”

Hundreds of people, chanting anti-violence slogans and wearing red or white bandanas around their heads in a show of grief, took to the streets of Mogadishu to condemn the deadly attack that has shocked Somalians.

“We have seen what the terrorists can mercilessly do by shedding the blood of innocent civilians,” Mohamed told the protesters after they ended their march at a square in southern Mogadishu. “We need to stand united against them”.

Activist Abukar Sheik added: “There is no house in which people are not crying today.”

The explosion occurred at a junction in Hodan, a bustling commercial district which has many shops, hotels and businesses in the city's northwest.

Security officials said hundreds of people had been in the area at the time of the blast, with police saying it was difficult to get a precise number of victims because the bodies had been taken to different medical centres while others had been taken directly by their relatives for burial.

As the rescue work continued, Somali President Mohamed Abdullahi Mohamed, better known as Farmajo, declared three days of mourning as he visited the attack site and then met with some of the wounded at a nearby hospital.

“Today's incident was a horrible attack carried out by Al-Shabab against innocent civilians that was not aimed at specific Somali government targets,” he said in a televised address to the nation.

“This shows how these violent elements are ruthlessly and indiscriminately targeting innocent people.”

'Whole area destroyed'

Although the Safari Hotel was popular, it was not one frequented by government officials ─ which have often been targeted by Shabab militants.

The devastation caused was widespread. Muhidin Ali, a Mogadishu resident who was close by at the time said it was, “the biggest blast I have ever witnessed, it destroyed the whole area.”

Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman al-Thani wrote on Twitter that the country's embassy had been badly damaged in the blast and one of its top officials wounded.

Meanwhile, the National Union of Somali Journalists said a freelance cameraman, Ali Nur Siyaad, had been killed and four other journalists wounded in the explosion.

The Red Cross in Somalia said five of its volunteers had also been killed during the blast many others wounded.

The Shabaab was forced out of the capital six years ago by African Union and Somali troops, and subsequently lost control of major towns across southern Somalia.

However, the militants continue to control rural areas and launch attacks on military, government and civilian targets in Somalia, as well as terrorist raids in neighbouring Kenya.

Saturday's blast came two days after Somalia's defence minister and army chief both resigned from their posts without explanation.