Flights at a major airport have been disrupted due to a "potential drone sighting" in the area.
Some flights were delayed at Manchester Airport and some were diverted to other airports while a police helicopter investigated the report of the sighting.
But nothing was found.
A Manchester Airport spokeswoman said: "Due to a report of a potential drone sighting in airspace near to the airport, some flights have experienced short delays and a small number of flights have diverted to alternative airports while Greater Manchester Police carried out an investigation using their police helicopter.
"Upon inspection, nothing was found. As the safety and security of all of our passengers is paramount, operations on runway one were suspended for 20 minutes. Runway two, which was unaffected, will remain open for an hour so normal traffic flows can resume."
John Mayhew, air traffic control company Nats' general manager for air traffic services at Manchester Airport, said: "Flying drones in the close vicinity to any airport without permission is completely unacceptable, with the reported sighting causing delays to inbound and outbound traffic and the diversion of a small number aircraft to other airports.
"The matter has now been referred to the police."
A UK Airprox (aircraft proximity) Board report last December described how a device believed to be a drone came within 20ft of an incoming Airbus A320 passenger plane at Heathrow airport.
The Airbus was 700ft from landing when the pilot reported seeing a small black object to the left of the aircraft, the report said.
The object appeared to be a small radio-controlled helicopter.
The object did not strike the plane and the pilot was able to make a normal landing in the incident, which occurred on the aftrnoon of July 22 2014.
Civil Aviation Authority (CAA) regulations state:
:: A drone must never be flown beyond the normal unaided 'line of sight' of the person operating it. This is generally measured as 500 metres horizontally or 400ft vertically;
:: A drone must always be flown at least 50 metres distance away from a person, vehicle, building or structure;
:: A drone must not be flown within 150 metres of a congested area or large group of people, such as a sporting event or concert.
So far, the CAA has successfully prosecuted two Unmanned Aerial Vehicle (UAV) operators relating to safety breaches and currently have another three investigations running.
The CAA is also working with several police forces across the country on similar drone-related investigations, which they are leading.
The CAA said that in the first instance the public should report any drone-related concerns to the police and it is for the Police to investigate any related matters, including anti-social behaviour or damage caused by drones.