A plane approaching Heathrow Airport is believed to have hit a drone before it landed safely, the Metropolitan Police has said.
The British Airways flight from Geneva was hit as it approached the London airport at about 12:50 BST with 132 passengers and five crew on board.
After landing, the pilot reported an object - believed to be a drone - had struck the front of the Airbus A320.
Aviation police based at Heathrow have launched an investigation.
Police said no arrests have been made.
If confirmed, it is believed to be the first incident of its kind in the UK.
A British Airways spokesman said: "Our aircraft landed safely, was fully examined by our engineers and it was cleared to operate its next flight."
The airline will give the police "every assistance with their investigation", the spokesman added.
A Civil Aviation Authority (CAA) spokesman said it was "totally unacceptable" to fly drones close to airports, and anyone flouting the rules can face "severe penalties, including imprisonment".
Steve Landells, from the British Airline Pilots Association (Balpa), said it had been "only a matter of time before we had a drone strike". He called for greater enforcement of existing rules.
Leo Kelion, Technology editor
Flying a drone near an airport can already be punished with up to five years in prison, and rules also forbid taking them above 400ft (122m) or near buildings and crowds of people.
But the latest incident will only add to the pressure for further steps to be taken.
The US recently introduced a compulsory registration scheme so any drone recovered from an accident can be traced back to its owner.
In addition, officials could make it mandatory for drones to run geo-fencing software - that would prevent them flying in restricted areas.
The Department for Transport has promised to publish a strategy for unmanned aircraft this year.
And pilots have also called for the DoT to fund tests into what would happen if a drone got sucked into an engine or crashed into a plane's windscreen.
Last month, the British Airline Pilots Association noted that while the threat of bird strikes had been well researched there was little data about how much damage a drone could cause a plane.
The incident follows a warning earlier this year by the head of the International Air Transport Association that drones flown by the general public are "a real and growing threat" to civilian aircraft.
Tony Tyler called for drone regulations to be put in place before any serious accidents occur.
The UK Air Proximity Board - which investigates near-miss incidents in UK airspace - said there have been a number of serious near-misses at UK airports involving drones.
Category A incidents - the most serious - were reported at Stansted, Heathrow, London City and Manchester airports last year.
Drone incidents at UK airports
- 17 April 2016 - A British Airways plane approaching Heathrow is believed to have hit a drone while in midair
- 28 November 2015 - The pilot of an A321 plane narrowly missed a drone hovering at 100ft above a runway at Gatwick Airport
- 30 September 2015 - A small drone helicopter passed within 30ft of the cockpit of an A319 plane while on the approach to Heathrow
- 22 September 2015 - A "quadcopter-type drone" missed the right-hand side of a B777 plane by about 25m while at 2,000ft after it left Heathrow Airport
- 13 September 2015 - A silver drone with a "balloon-like" centre missed an E170 aircraft by about 20m, while the plane was approaching London City Airport over the Thames
- 13 September 2015 - A drone flew over the top of a B737 aircraft while at 4,000ft, missing it by about 5m, shortly after it left Stansted
- 27 August 2015 - A DO328 aircraft flew within 50ft of a drone while approaching Manchester Airport at 2,800ft
Source: The UK Airprox Board