At least 34 people were declared missing in Cameroon on Monday after a military ship sank off the country’s coast in the Atlantic on Sunday. Defence Minister Joseph Beti Assomo said there were 37 people on board the vessel, which was on a routine mission to the oil-rich Bakassi peninsula in the Gulf of Guinea when it went underwater, AP reported.

Military personnel are carrying out search operations. Three soldiers have been rescued so far, the minister said.

While how the ship sank remains unclear, reports suggest that the vessel capsized because of unexpectedly turbulent waters, according to Cameroon Radio Television.

The control centre raised an alarm after losing contact with the military vessel. Patrols were sent out immediately to locate the ship, read a press release from the Defence Ministry. Helicopters are believed to have been able to spot traces of fuel, after which patrols were sent to the likely location of the wreckage.