Four Americans and a Kenyan pilot were killed when their helicopter crashed shortly after taking off from a remote island in Lake Turkana in a national park in northwest Kenya, officials said.

The aircraft came down on Monday in Central Island National Park at around 8pm local time (21:00 GMT) on Sunday, Kenya's National Police Service said on its Twitter feed, killing all on board.

The cause of the crash had yet to be determined.

The Kenya Civil Aviation Authority (KCAA) said two helicopters took off from the island on Sunday night heading for Lobolo Camp on the mainland. Rescuers found the wreckage early on Monday morning, Gilbert Kibe, director general of the KCAA, said in a statement.

"Shortly after take-off, unfortunately, one of the helicopters, a Bell 505, registration 5YKDL, lost contact and crashed on the island," Kibe said.

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

The United States embassy in Nairobi confirmed the deaths of the four Americans and the names of three of them: Anders Asher Jesiah Burke, Brandon Howe Stapper and Kyle John Forti.

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. (Aljazeera)