Local media footage also showed ambulances and fire trucks at the scene.
A strong explosion of unknown origin shook the busy shopping street of Istiklal in Istanbul on Sunday, leaving six people dead and wounding dozens more, President Recep Tayyip Erdogan said. Turkey's vice president said a suicide bomber carried out the attack.
"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 told a televised press conference.
"The relevant units of our state are working to find the perpetrators... behind this vile attack," he said.
Police cordoned off the area, where crowds were dense on Sunday afternoon, and helicopters were flying over the city centre as sirens were sounding.
"I was 50-55 metres (yards) 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.
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 were visible.
The explosion occurred shortly after 4:00 pm (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.
Istiklal Street had already been hit in the past during a campaign of attacks in 2015-2016 that targeted Istanbul.
Claimed by the Islamic State group, those attacks killed nearly 500 people and injured more than 2,000.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
