Six people were killed and 53 others were wounded on Sunday when an explosion rocked a busy pedestrian street in central Istanbul in an incident President Tayyip Erdogan called a bomb attack that “smells like terrorism”.

Ambulances raced to the scene on the packed Istiklal Avenue, which police had quickly cordoned off. The area, in the Beyoglu district of Turkey’s largest city, had been crowded as usual at the weekend with shoppers, tourists and families.

“I was 50-55 metres away, suddenly there was the noise of an explosion. I saw three or four people on the ground,” witness Cemal Denizci, 57, told AFP.

“People were running in panic. The noise was huge. There was black smoke. The noise was so strong, almost deafening,” he said.

Parents swept their children up into their arms as they fled the area. Istanbul governor Ali Yerlikaya tweeted that four people died and 38 were wounded according to preliminary information.

Authorities have given no indication of what caused the explosion.

According to an AFP video journalist on the scene, the police have established a large security cordon to prevent access to the damaged area for fear of a second explosion.

A massive deployment of security forces equally barred all entrances, while a heavy deployment of rescue workers and police was visible.

A Reuters reporter saw a helicopter overhead and several ambulances in nearby Taksim Square.

“When I heard the explosion, I was petrified, people froze, looking at each other. Then people started running away. What else can you do,” said Mehmet Akus, 45, a worker in a restaurant on Istiklal.

“My relatives called me, they know I work on Istiklal. I reassured them,” he said.

The nearby Kasimpasa police station told Reuters all crews were at the scene but gave no further details.

Local media said crime inspectors were on the scene and Anadolu reported that the Istanbul chief public prosecutor’s office had launched an investigation into the blast.

The explosion occurred shortly after 4pm (1300 GMT) in the famous Istiklal shopping street which is popular with locals and tourists.

According to images posted on social media at the time of the explosion, it was accompanied by flames and immediately triggered panic, with people running in all directions.

A large black crater was also visible in those images, as well as several bodies lying on the ground nearby.

The Turkish Red Crescent said blood was being transferred to nearby hospitals.

Turkey’s RTUK regulator imposed a broadcast ban on coverage of the blast around an hour after it occurred.

“My condolences to those who lost their lives in the explosion on Istiklal Avenue,” Mayor Ekrem Imamoglu said on Twitter.

Istiklal Street had already been hit in the past during a campaign of attacks in 2015-2016 that targeted Istanbul.

Claimed by the militant Islamic State group, those attacks killed nearly 500 people and injured more than 2,000.

Erdogan says attack ‘smells like terrorism’

President Recep Tayyip Erdogan on Sunday condemned the “vile attack” that ripped through central Istanbul, and which he said killed six people and wounded dozens of others.

“The relevant units of our state are working to find the perpetrators… behind this vile attack,” Erdogan told a televised press conference.

He also said initial signs pointed to a “terror” attack in the explosion in Istanbul which wounded 53 others.

“It might be wrong if we say for sure that this is terror but according to first signs… there is a smell of terror there,” Erdogan said.

“The attempt to take over Turkey and the Turkish nation through terrorism will not reach its goal today or tomorrow,” he added.

Pakistan extends condolences

Politicians across parties extended their condolences and expressed their regret at the incident.

“Government and people of Pakistan express deepest condolences to the brotherly people of Turkiye at the loss of precious lives and send prayers for the speedy recovery of the injured,” tweeted Prime Minister Shehbaz Sharif.

Foreign Minister Bilawal Bhutto Zardari said he was “deeply saddened” by the incident and Pakistan stood in “complete solidarity” with the Turkish people in their hour of grief.

“The world must take practical measures to end terrorism and extremism,” said former president Asif Ali Zardari, adding that attacking innocent people was “unforgivable”.

PTI Chairman Imran Khan, in a video address, also expressed regret and prayed for the speedy recovery of the injured and their families.