Four of the busiest border crossing points between Canada and the United States are closed after a vehicle exploded at a U.S. checkpoint in Niagara Falls. 

The FBI confirmed it is investigating an explosion, which took place on the U.S. side of the Rainbow Bridge crossing in upstate New York.

Videos posted to social media show smoke and flames emanating from the checkpoint complex at the crossing, which spans the Niagara River. 

New York Gov. Kathy Hochul said in a statement that she had been fully briefed and was monitoring the situation closely. 

Media reports suggest the vehicle was trying to enter the U.S. from Canada. All four crossings between Canada and New York state are closed.

CNN is reporting that customs officials had redirected the vehicle for a secondary screening just prior to the explosion.

The incident comes just one week after FBI director Christopher Wray warned a congressional committee about a heightened risk of extremism linked to the Israel-Hamas war.

Prime Minister Justin Trudeau's office said in a statement that he has been briefed by his national security and intelligence adviser about "the situation in Niagara Falls."

It said the public safety minister, the RCMP and the Canada Border Services Agency are "fully engaged and providing all necessary support," and "we are in contact with the U.S. officials."

"Our provincial law enforcement is actively engaged in assessing the situation," Ontario Premier Doug Ford said in a statement. 

"They are working with local law enforcement and are providing support as required."

This report by The Canadian Press was first published Nov. 22, 2023.

— With files from The Associated Press.