Four American tourists and a Kenyan pilot were killed when their helicopter crashed on an island in a lake in northwest Kenya, police said Monday.

The helicopter crashed Sunday evening at Central Island, a volcanic island on Lake Turkana, Kenya's national police said in a statement.

"Available information indicates that two helicopters had landed earlier at Labolo tented camp on the national park's island, however [only] one managed to clear the area safely," the statement added.

The wreckage of the helicopter was recovered in the early hours of Monday.

The cause of the accident remains unknown.

Police did not identify the victims, saying next of kin had to be notified first.

The crash comes less than a month after three Americans were among five who died in a plane crash in the west of the country.