Turkish President Recep Tayyip Erdogan said an explosion that occurred in central Istanbul on Sunday leaving at least six dead and 53 injured is an "attack."

"The relevant units of our state are working to find the perpetrators," Erdogan said.

On Twitter, Governor of Istanbul Ali Yerlikaya initially wrote after the blast that "There are casualties and injuries." He later tweeted, "According to initial reports, 4 people lost their lives and 38 were injured in the explosion that took place on Istiklal Street."

Istanbul mayor Ekrem Imamoglu said, "It is essential to assist our police and health teams regarding the explosion on Istiklal Street, and to avoid posts that may cause fear and panic."

What do we know so far?

Videos shared on social media showed multiple people on the ground amid blast damage. The footage showed ambulance and police arriving on the scene.

Turkish media reports indicated the blast occurred at 4:20 p.m. local time (1330 GMT). Video posted online taken at the time of the blast showed a fireball overwhelm the crowded street as pedestrians strolled before abruptly turning, many running scared.

Turkey's media watchdog, the Supreme Board of Radio and Television, imposed temporary restrictions on reporting on the blast and its aftermath shortly after the incident. In the past, such restrictions have been in place following similar incidents.

On social media, users said Istiklal Street, just off Taksim Square, was cordoned off as shops were closed. A Reuters reporter observed a helicopter over the blast scene.

Cemal Denizci, 57, told AFP, "

Istiklal Street runs through the central district of Beyoglu, home to many foreign residents and is frequented by tourists.

Turkey's state news agency Anadolu reports five prosecutors have been assigned to investigate the cause of the blast.

Previously n 2016, a suicide bomber detonated on Istiklal, killing four and injuring 39.

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