It is believed that a passenger allegedly threatened to blow up the aircraft after other passengers tried to intervene in a row he was involved in.
Murtaza Ali Shah, a journalist, said he had spoken to a friend on board the plane, Fakhir Iqbal, a political activist, who was sitting behind the man who made the threat. Mr Shah said his friend told him: "Two guys started a row with a girl and lots of other people. "Some people tried to calm them and asked them not to be rowdy and abusive. "Fakhir told them to calm down.
"They said, 'Don't bloody speak to us or we will blow up the plane".
"The crew came and spoke to them and they were openly threatening the staff. "Fakhir went to other crew members and told them they were making threats."
May 24, 2013
UPDATE: Umari Nauman said: "The cabin crew informed us that basically they tried to come into the cockpit a few times and because they had been asked not to do that they got into a bit of an argument with the crew and made a few threats."
Update: A PIA spokesman said the airline was repeatedly unable to contact the pilot. The arrested men - Kashaf and Zaroon - are aged 30 and 41 and have been taken to a police station for interview by detectives. They tried to enter the cockpit during the flight.
Update: Wajid Hasan, Pakistan's High Commissioner to the United Kingdom, said the two passengers "got into an altercation with air stewardesses and threatened to blow up the plane." The air stewardesses contacted the pilot, who contacted UK air traffic control authorities, who then scrambled the fighter jets, he said.
"So far nothing has been found," he said. "All the passengers are off the aircraft and are being screened, as would be normal, by immigration authorities," he said, and the cargo is also being searched. The process is expected to take about four hours, he said, after which the passengers will fly on to Manchester.
Update: Passenger: "The two men arrested tried to break into the cockpit."
Update: (PIA) spokesman Zufiqar Bijarani: "We have been told there may have been a bomb threat."
Another Pakistan International Airlines spokesman Mashood Tajwar said the airline had been unable to contact the pilot of the Flight P709 despite repeated attempts. He said 297 passengers and 11 crew members were on the diverted plane.
Update: A threatening phone call was made to the UK's air traffic control.
Update: Pilot or crew on flight PK709 may have sent out a Quick Reaction Alert triggering the interception.
The plane is on the ground and has been isolated in a part of the airport away from passenger planes.
Update: The aircraft was originally heading towards Manchester when it was re-routed and sent back out to the North Sea before travelling to Stansted. Reports say the plane has now landed.
An incident has occurred on an aircraft. Police and partners are responding.
A Ministry of Defence spokesman said: "A Typhoon aircraft has been launched to investigate an incident involving a civilian aircraft within UK airspace." He added that the Typhoon is from RAF Coningsby in Lincolnshire.
Pakistan International Airlines said the plane had landed safely at Stansted, but they do not have communications with the pilot.
Update: Two men have been removed from a Pakistan International Airlines flight and arrested on suspicion of endangerment of an aircraft after the plane was diverted and was escorted by an RAF Typhoon.
The Ministry of Defence has confirmed that an RAF Typhoon fighter jet escorted the diverted Pakistan International Airlines flight from Manchester to Stansted Airport. The airline has confirmed the decision was taken for security reasons.
Pakistan International Airlines PK709 was the scheduled 0935 Lahore to Manchester flight. There are thought to be 297 passengers on board. It is understood that the incident happened around 10 minutes before the plane was due to land in Manchester at 2pm.
A UK fighter jet was scrambled to escort a Pakistan International Airlines flight as it was diverted Friday from northwestern England's Manchester Airport to London's Stansted Airport.
The plane was coming from Lahore, Pakistan, a Manchester airport representative said. Early indications show Friday's diversion of the flight to London's Stansted is not a terror-related incident, a security source in London said.
Zulfiqar Bijarani, of Pakistan International Airlines, told CNN the airline did not yet know what caused the diversion. Essex Police, which covers the area near Stansted airport, said the plane has now landed at Stansted Airport.