An ONGC helicopter carrying nine persons including two pilots, on Tuesday fell into the sea while attempting to land on a company's rig in the Arabian Sea, the company said adding that six persons have so far been rescued.

Six of the nine persons so far have been brought to safety and attempts are on to rescue others, a company official said.

The helicopter, which had six ONGC personnel onboard, and one belonging to a contractor working for the company, was forced to land using the floaters that are attached to choppers that carry personnel and material from shore to offshore installations.

The chopper was attempting to land at the rig, located some 50 nautical miles from the Mumbai coast, when the incident took place. About 1.5 km from the landing zone on the rig, the chopper fell into the sea, the official said.

The circumstances that led to the incident were not immediately clear. Other details too were awaited, he said.

ONGC has several rigs and installations in the Arabia Sea that are used to produce oil and gas from reservoirs lying below the seabed.

ONGC deployed vessels from nearby installations to pull out the personnel onboard the helicopter.

A rescue boat from the rig Sagar Kiran, near which the helicopter made the emergency landing, rescued at least one person, the official said.

ONGC vessel Malviya-16 rescued four persons.

Details of the incident are so far sketchy.

"#Helicopter mishap in #Arabian Sea near #ONGC rig Sagar Kiran in #Mumbai High; carrying 7 passengers & 2 pilots," ONGC tweeted. "Six persons have been rescued so far."