ISTANBUL, July 12 (Xinhua) -- A forest fire on Sunday erupted on an island off the coast of Turkey's biggest city Istanbul, local media reported.

The fire of unknown causes broke out in Heybeliada, one of the main islands of an archipelago in the Marmara Sea, known as the Princes' Islands, the NTV broadcaster said.

Many firefighters, helicopters, and fire intervention vessels have been sent to the scene, according to NTV.

A massive smoke can be seen from many locations on the Asian side of the city, several videos posted on social media revealed.

No casualties have so far been reported, press reports said, noting that an investigation has been launched into the incident.

(Photo: Agencies)