London (AFP) - A British Airways plane struck an object believed to be a drone as it was coming in for landing at Heathrow, Europe's busiest airport, police said.

An investigation has been launched into the incident, which follows a string of near misses involving drones and is believed to be the first case of a collision in Britain.

The plane, an Airbus A320 with 132 passengers and five crew on board, was on its final descent into Heathrow when it was struck.

"A pilot on an inbound flight into Heathrow Airport from Geneva reported to police that he believed a drone had struck the aircraft," a spokeswoman for London's Metropolitan Police said.

"The flight landed at Heathrow Terminal Five safely. It transpired that an object, believed to be a drone, had struck the front of the aircraft".

A BA spokesman said the plane had been examined after landing and was cleared to operate its next flight.

"Safety and security are always our first priority and we will give the police every assistance with their investigation," the spokesman said.

The UK Airprox Board, an air safety agency, said last month there were 23 near-misses between drones and aircraft in the six months between April and October last year.

In one incident on September 22, a Boeing 777 reported narrowly passing a drone as it was taking off.

Investigators concluded that the drone was at the same height as the aircraft and within 25 metres of it.

A drone then came within a few metres of an Airbus A319 landing at Heathrow only a few days later on September 30.

"It was only a matter of time before we had a drone strike given the huge numbers being flown around by amateurs who don't understand the risks and the rules," said Steve Landells, flight safety specialist at the British Airline Pilots Association.

A spokesman for the Civil Aviation Authority said it was "totally unacceptable" to fly drones close to airports and anyone flouting the rules faced possible imprisonment.

Under British legislation, drones cannot be flown near planes, helicopters and airports and must be kept below 400 feet (122 metres).