A vehicle has exploded on a bridge that connects the US and Canada near the Niagara Falls, leading to the closure of four border crossings in the region.

The incident took place on the Rainbow Bridge one day before the Thanksgiving holiday in the US, one of the busiest travel days of the year.

"As this situation is fluid, this is all we can say at this time," the FBI said in a statement.

Two people who wereinside the vehicle have died, according to US media.

The incident involved a vehicle that was "coming into" the US, the city of Niagara Falls said in a statement, although officials later said there was conflicting information about where the vehicle camefrom.

An official told CBS, the BBC's US partner, that it is too early to say what caused the vehicle to explode.

The incident took place just around 11:30 local time (16:30GMT).

New York State police are working with the FBI Joint Terrorism Task Force to monitor all points of entry to New York, said Governor Kathy Hochul.

"State agencies are on site and ready to assist" in the federal investigation, she said on X, formerly Twitter, adding that she is travelling to Buffalo to meet with law enforcement.

Speaking in the House of Commons, Prime Minister Justin Trudeau said the government is working with the US to ensure that travellers remain safe.

Additional security measures are being brought to border crossings across the country, he said.

"We are taking this extraordinarily seriously," Mr Trudeau added.

President Joe Biden, who is at his home in Delaware for the Thanksgiving holiday, has also been briefed on the incident, according to the White House.

At least one person was injured in the incident.

James Suitor, director of public safety and emergency management at Niagara Falls Memorial Medical Center, said a male patient was brought to the hospital.

He was "treated and evaluated" in the emergency room and his injuries were deemed by doctors to be non-threatening.

The bridge connects Ontario with New York and links the cities of Niagara Falls, US with Niagara Falls, Canada.

In addition to the Rainbow Bridge, the incident has led to the closure of three other international border crossings in the region.

The Peace Bridge, Lewiston-Queenston Bridge, and Whirlpool Bridge are also closed in both directions, officials say.

Security officials at the Buffalo airport, located 20 miles (32km) from the bridge, have closed the airport to incoming and outgoing flights.

Witnesses told the Niagara Gazette newspaper that they heard what sounded like an explosion and a cloud of smoke shortly before police arrived.

"We heard something smash," one witness said. "We saw fire and big, black smoke."

An eyewitness from Ontario, Mike Guenther, said he saw a car speed by at 100mph (160km/h) before flying into the air and erupted into a "fire ball". (BBC)