At least 35 people were killed and over 40 injured when a gunman opened fire inside a nightclub in Istanbul shortly after midnight on Sunday, Istanbul governor Vasip Sahin said.

Sahin called it a "terror attack."

Between 700 and 800 club goers celebrating New Year's Eve were said to have been present at the Reina nightclub in the Ortakoy neighborhood when the attack took place.

Police forces have been dispatched to the scene and cordoned off the area about three kilometers away from the nightclub.

As many as 60 ambulances also rushed to the scene.

The whereabouts of the attacker are still unknown.

There have not been any claims of responsibility.