Four people were killed after a rescue helicopter collided in mid-air with a small plane in Germany.

The accident happened on Tuesday (23 January) near to Philippsburg in south west Germany, not far from the French border.

Both aircraft came down over a gravel pit on the outskirts of the town of 13,000 people, which is the site of one of Germany's nuclear power plants. No other casualties have been reported.

German Air Rescue announced in a press release: "According to current knowledge, the two pilots of the DRF Luftrettung and two passengers of the small plane were killed. The cause of the accident is still completely unknown."

DRF Luftrettung is Germany's civil air rescue service.

Police and emergency services are currently working at the scene to establish the cause of the accident, which happened at around 1pm local time.

A police spokesman: "We do not know yet who was sitting in which machine. Right now we need to get an overview of the situation first."

Mid-air collisions are extremely rare in Germany.

One of the worst to ever occur in the country was in 2002 when a passenger jet and a cargo jet hit each other over Uberlingen, southern Germany, killing all 71 people on board the two planes.