A helicopter has crashed into the sea off east Yorkshire, British police have said.

A coastguard officer has been winched down to assess the crash site, and lifeboats from Flamborough and Bridlington are also searching the area.

The helicopter is not believed to be from the British or US military, with an eyewitness describing it as a "small, white" aircraft. There have so far been no details on the condition of those on board.

Ron Marwood, from the local golf club, which fringes the cliffs, described the helicopter as probably having just two to four seats.

He told Sky News he had heard a change in engine noise and then it "just disappeared".

"It was flying along quite happily. The engine noise seemed to change - that was the first I sort of took notice of it," said Mr Marwood.

"It appeared to be coming in, as if to try and get in close to the cliff and maybe land on the cliff, because it's all cornfields and that. But it disappeared below the level of the cliff."

Visibility was around three to four miles and emergency services arrived within minutes, Mr Marwood said. Coastguard, police and the ambulance service were called to the scene at 1:39pm.

A Yorkshire Ambulance Service spokeswoman said an air ambulance, an ambulance, the RAF and rapid response vehicles were in attendance.

A team from the UK Air Accidents Investigation Branch has also been dispatched.

Members of the public are being warned to stay away from the crash site due to dangerous cliff edges and aviation fuel in the water.