Eight dead and one has been injured when a helicopter bound for an offshore oil platform crashed in Louisiana's marshlands, Sunday afternoon.

The helicopter, operated by PHI Inc., one of the Gulf Coast's leading providers of helicopter services to offshore oil platforms, crashes after taking off, which happened about 100 miles southwest of New Orleans.

The cause of crash and the helicopter type is still unknown, said Richard Rovinelli, a spokesman for the company.

Identities of the injured have not been released.

It's the second tragic accident for the company within a year. In June, a PHI Air Medical helicopter crashed in Texas, killing four.