A British Airways flight was forced to land in Montreal after reportedly receiving a bomb threat.
The 747 took off from Las Vegas and was bound for Heathrow when it made the landing on Wednesday.
People on Twitter uploaded photos that showed a huge number of emergency vehicles on the ground when it landed and people leaving the plane.
According to City AM, there were more than 300 people on board.
The passengers disembarked and media reported it was due to a bomb threat against the plane.
The claim it was a bomb threat was repeated by a woman on Twitter who appeared to have been on board.
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The passengers have reportedly been accommodated overnight.
British Airways refused to comment on whether a bomb threat was made to the plane, saying: "We would never discuss matters of operational security."
A spokesman said: "Our flight from Las Vegas to Heathrow landed safely this morning at Montreal and customers left the aircraft as normal after the Captain took the decision to divert the aircraft as a precaution.
"The safety and security of our customers, crew and aircraft are our highest priorities at all times.
"We are looking after the customers and will provide hotel rooms for them and will rebook them to other flights as soon as we can. We are working with the Canadian authorities and giving them our fullest support."