Authorities say a vehicle has exploded at a checkpoint on the American side of a U.S.-Canada bridge on the Niagara Falls.Canadian Prime Minister Justin Trudeau called Wednesday's blast “a very serious situation.”There was no immediate information on whether anyone was injured or on the cause of the explosion.Four border crossings in the area are closed as a result, and the Buffalo-Niagara International Airport began security checks on all cars.The FBI’s field office in Buffalo said in a statement that it was investigating the explosion Wednesday on the Rainbow Bridge. It connects the two countries across the Niagara River.Photos and video footage taken by news organizations and posted on social media showed a security booth that had been singed by flames.
