Istanbul governor Ali Yerlikaya tweeted that four people died and 38 were wounded according to preliminary information following a strong explosion of unknown origin rocked the busy shopping street of Istiklal Avenue in Istanbul, Turkey on Sunday.

Within the hour President Erdogan in a brief statement condemned the “vile attack” and announced that the number of dead has risen to six.

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.