A Paris-bound Air France flight from San Francisco was diverted to Montreal late Monday due to what the airline described as an "anonymous threat".

Air France said Flight 83 landed at Montreal-Pierre Elliott Trudeau International Airport without incident shortly before midnight local time and local authorities were inspecting the plane. The airline described the early landing as "a precaution."

Air France tweeted Tuesday: "after a full security search, false alert confirmed by local authorities following an anonymous threat."

At least 15 fire trucks and police cars met the plane, and Canadian authorities were verifying the aircraft, passengers and baggage. Air France said an investigation will be carried out into the origin of the threat, and promised to send passengers safely to their destinations. Spokeswoman Ulli Gendrot said all passengers were off the plane within a few hours of landing.

According to the flight tracking website FlightAware, the Boeing 777 took off from San Francisco International Airport shortly after 3 p.m. local time and was due to land in Paris Tuesday morning. 

Passenger Thomas Serval posted pictures of the inside of the cabin as passengers were taken off in small groups. Officials at the Montreal Airport told Canadian media the flight was carrying 231 passengers and 15 crew members. 

 

Passenger Gilles Raymond of San Francisco told the Associated Press that the pilot announced about five hours into the flight that they needed to land in Montreal because of technical reasons. Raymond said the pilot had added that authorities would have to do a thorough security check of the plane and passengers and that everyone would have to disembark.

"Everyone is pretty relaxed," Raymond said while still inside. "There was no panic, no stress. Everyone is waiting in their seats. Some people are sleeping, and some are checking their phones or eating ice cream that the flight attendants gave them."

He said passengers spent at least an hour on board the plane during verifications: "They told us they will check every passenger and that we may spend the night here."

The aircraft was the third Air France flight to be diverted in less than a month due to threats. On the night of Nov. 17, two Paris-bound flights received anonymous telephoned bomb threats. One flight, originating from Los Angeles, was diverted to Salt Lake City; the other, from Washington Dulles Airport, was diverted to Halifax, Nova Scotia. U.S. and Canadian authorities gave both flights the all-clear after searching the plane and the passengers. 

France remains in a state of emergency after ISIS terrorists killed 130 people in a series of coordinated shootings and bombings across Paris Nov. 13.

The Associated Press contributed to this report.