An incoming plane has been escorted into Manchester airport by the RAF, after a passenger apparently handed a note to crew members claiming to be carrying a bomb.
A man pulled from the QR23 flight has been arrested on suspicion of making a hoax bomb threat, a spokesman for Greater Manchester Police said.
The Police said the RAF involvement came "as a result of information received by the pilot about a possible device on board".
The passenger being removed from the plane by police officers
It is thought that the plane involved was a Qatar Airways Airbus A330 and that the RAF plane was a Typhoon from RAF Coningsby in Lincolnshire. Qatar Airways said 269 passengers were on board.
A passenger, Josh Hartley, live-tweeted the incident and took a photo of the Typhoon escort.
He said there were armed police outside the plane and uploaded a photo of fire engines gathered nearby.
Another passenger tweeted an image that appeared to show the person being removed.
Plane passenger Aurang Zeb, 60, returning from a holiday to his home in Bradford, said: "I thought there was something wrong because there was a jet flying so near."
Zeb said the plane landed and was taken to an area well away from the terminal and other planes, where they waited for 45 minutes then moved again closer to the terminal. Then I saw all the police with guns. Lots of police everywhere. Kids were crying, some people looked very worried because of rumours there's a bomb on the plane."
Zeb said two armed police then came on and removed the suspect passenger. "They sat him up and said, 'Put your hands up'. He did not say anything. People were still worried something might be on board. There was a rumour of a bomb on the plane so people are scared, thank God for that not happening."
William McDade, 60, from Perth, Australia, over visiting family in Elderslie near Glasgow, said: "When you are sitting on a plane there's not much you can do, you have just got to sit there. I just thought it was an unruly passenger, a drunk. When he stood up he didn't appear to be drunk, he put his hands on his head straight away. There was no commotion on the plane whatsoever."
Manju Geo, from India visiting family in Stoke said: "At least two police came on and took one man off called Mr Roy.
"We were told he was writing some notes on the flight and the air hostess found that."
Matthew Cox, 24, from Chester, said after landing the pilot addressed the passengers: "We were told by the pilot everybody should stay seated, nobody should move, then police came inside the plane. They arrested the man and took him and the police came on again and said, 'Go' three rows at a time."
Passengers said two armed police arrested the suspect, who was ordered to put his hands on his head before being led away. Cox added: "He was very very compliant. They asked him to put his hands on his head and he submitted himself to a search. There was a general kind of nervousness but there was no full scale panic once on the ground."
Cox said all the passengers' luggage was searched before they were allowed to leave the airport.
Chief Superintendent John O'Hare said in a statement: "An incoming plane has been escorted into the airport by the Royal Air Force as a result of information received by the pilot about a possible device on board.
"We don't know how genuine this threat is but it is absolutely vital we deal with the situation as a full emergency.
"As a result, people will see the police and other agencies at the airport and on the airfield.
"At this time I would urge them not to be alarmed. Our response will be as comprehensive as it is proportionate with the safety of those on board and in and around the airport our paramount concern."
Flights to the airport are being diverted to Leeds Bradford Airport, it has been reported.
The plane (left) being escorted in by an RAF Typhoon (right)
The RAF Typhoon, photographed from the plane by a passenger
At the airport terminal loved ones of the passengers waited anxiously for news. Pauline Cox, from Chester, waiting for her son, Matthew Cox, 24, travelling back after a three-week trip to Thailand, said: "Nobody has been out from Manchester Airport to tell us anything. Parents have been waiting, two, three hours. When we asked we were told they were in a remote location for security reasons. We have heard there's a bomb and our innocent children are sat on that plane."
Cox said her son and the other passengers were going through passport control and baggage reclaim with all the other travellers. "I'm just so frustrated they have been through that ordeal and just treated with not the respect they deserve, that's not how you treat victims. They are victims in this."
Arthur Smee, 58, a hospital porter from Penmaenmawr, North Wales, was waiting for his daughter, Lisa, 25, to arrive when he heard about a bomb scare on the plane. "Some people were stood around talking and some had pictures of the plane being followed by a military plane - you just think the worst don't you?" he said. "I'm just glad she got in touch. She said armed police have been on the plane and taken somebody off. They were just sat there for ages then put on a bus."
Witness Paul Bell, who was on his way to the airport in a taxi, told Sky News that he saw the RAF Typhoon meet the passenger plane.
He said: "We heard the fighter jet circling over Stockport, and literally 10 minutes later we saw the plane coming in being followed by it.
"We saw the (RAF Typhoon) coming in, literally flying around the aeroplane.
"It then pinged up on the sat nav that the airport is on lock-down.
"There are lots of people hanging around, checking their phones. We're stuck in a massive traffic jam. There are no planes landing or taking off."
Authorities are following "standard procedures" in dealing with a possible threat, said David Kaminski-Morrow, the air transport editor of Flightglobal publication.
He said: "In situations like these, the plan is always to get the aircraft down at the nearest available landing site. It could be that a threat could have been phoned in and passed on to the captain. It could be that someone on board has spotted something.
"In any event, no one wants to take any chances."
An RAF spokesman said later that the plane had landed safely and the incident was being handled by civilian authorities.
He said: "We can confirm that Typhoon aircraft were launched from RAF Coningsby in their quick reaction alert role this afternoon to investigate a civilian aircraft whose pilot had requested assistance.
"The aircraft was escorted to Manchester where it landed safely. This incident is now being handled by the civilian authorities."
The airline said in a statement: "Qatar Airways can confirm that flight QR23 from Doha to Manchester, an Airbus A330-300, landed safely at Manchester Airport ahead of its scheduled arrival time of 1315.
"There were 269 passengers and 13 Qatar Airways crew on board.
"The crew on-board had received a threat about a possible device on board and Qatar Airways immediately took all the necessary precautions to alert British authorities.
"The crew is now fully assisting police at the airport with their inquiries. The safety and well-being of our passengers and crew is our top priority. As this is a matter of a police investigation, we cannot comment further at this time."