An Air France flight bound for Paris was diverted to Montreal last night after an anonymous threat was received, airport officials confirmed.

Flight 083 from San Francisco made an unscheduled stop in Montreal just after 11:20 p.m. ET, said Francois Asselin, a spokesman for Aéroports de Montreal. 

Air France confirmed around 4:45 a.m. that the threat was a false alarm.

The plane left for Paris around 6 a.m.

"We were told we had to be diverted for operational reasons by the captain," passenger Thomas Serval told CBC News. "We were anxious when we landed safely."

The Boeing 777-300ER was carrying 231 passengers and 15 staff members. The pilot decided to land in Montreal out of precaution, and the plane stayed on the tarmac for some time with passengers on board.

Police and firefighters were called to the scene at Pierre Elliott Trudeau International Airport, according to standard procedure.

Air France-Trudeau Airport

There were just under 250 passengers and crew on board the Boeing aircraft travelling from San Francisco to France before the unscheduled stop in Montreal. (Jean-Claude Taliana/SRC-CBC)

Gilles Raymond told The Associated Press that he and his fellow passengers spent at least an hour on the plane during verifications after being originally told the diversion was for "technical reasons."

"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."

It is not the first time the airline's flights have been diverted since the Nov. 13 attacks in Paris that killed 130 people and left hundreds injured.

On Nov. 17, flights bound for France were diverted to Halifax and Salt Lake City, Utah due to anonymous threats later found to be baseless after a sweep of the planes.

With files from The Associated Press