Saipem S.p.A. reported Tuesday that its jack-up drilling rig, the Perro Negro 6, capsized and sank offshore Angola after the seabed beneath one of its three legs collapsed.

The incident occurred Monday night during rig positioning on location near the mouth of the Congo River, between the coasts of Angola and the Democratic Republic of Congo, Saipem said in a statement. The rig had not yet commenced drilling when it collapsed, the statement added.

Saipem says that the Perro Negro 6 tilted suddenly Monday night after the seabed collapsed beneath it, causing hull damage and the rig to take on water. It later capsized and sank in approximately 40 meters of water at 10.30 AM CEST Tuesday after all personnel had been evacuated, Saipem said.

Of the 103 crew members on board at the time of the collapse, 6 incurred minor injuries and one is reported missing.

So far no environmental impacts have been reported.

Saipem emergency response team is mobilised and is working closely with the Angolan Authorities and the Client’s operational team.

The Perro Negro is under contract with Chevron Corporation through early 2015.

The rig was built by Labroy Shipyard in Batam, Indonesia in 2009 and can drill to a depth of 30,000 feet in 350 feet of water.