At least six people have been killed and 53 injured after an explosion on a busy pedestrian street in central Istanbul, Turkey’s president has said.

People ran away following the blast on Istiklal Avenue in the Taksim area.

A video posted online showed flames erupting and a loud bang.

President Recep Tayyip Erdogan called the explosion a “bomb attack” and said six people were killed and 53 wounded.

Speaking before his departure to the G-20 summit in Indonesia, Mr Erdogan said the explosion was a “treacherous attack” and its perpetrators would be punished.

Istanbul’s governor Ali Yerlikaya also tweeted the death toll and said the injured were being treated.

He said: “Unfortunately, in the explosion that took place on Istiklal Street today, the number of dead increased to six and the number of injured to 53.

“We wish God’s mercy on those who lost their lives and a speedy recovery to the injured.”

He said the explosion occurred around 4.20pm local time (1.20pm GMT).

State broadcaster TRT showed videos of ambulances and police headed to the scene.

Social media users said shops were shuttered and the avenue closed down.

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

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

The cause of the blast was not immediately known.

Five prosecutors have been assigned to investigate the explosion, state-run Anadolu news agency said.

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

Turkey’s RTUK regulator imposed a broadcast ban on coverage of the blast around an hour after it occurred. It prevents broadcasters from showing videos of the moment of the blast or its aftermath.

Istiklal Avenue is a pedestrian thoroughfare popular with tourists and locals and is lined with shops and restaurants.

Turkey suffered several deadly bombings between 2015 and 2017 by Islamic State and outlawed Kurdish groups.