A vehicle exploded at a checkpoint on the American side of a U.S.-Canada bridge in Niagara Falls Wednesday, prompting the closing of four border crossings in the area, authorities said. There was no immediate information on whether anyone was injured or on the cause of the explosion. “This is obviously a very serious situation in Niagara Falls,” Canadian Prime Minister Justin Trudeau said in Parliament, as he excused himself from Question Period in the House of Commons to be briefed further. “We are taking this extraordinary seriously,” he added. The blast happened on the U.S. side of the Rainbow Bridge, which connects the two countries across the Niagara River. Three other bridges between western New York and Ontario were quickly closed as a precaution, and the Buffalo-Niagara International Airport began security checks on all cars and told passengers to expect additional screenings. Trudeau said that “additional measures” were being contemplated and activated at border crossings across Canada. The FBI’s field office in Buffalo said in a statement that it was investigating the blast, and investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives were also responding to the scene. Photos and video taken by bystanders and posted on social media showed thick smoke, flames on the pavement and a security booth that had been singed by flames. Videos showed that the fire was in a U.S. Customs and Border Protection area just east of the main vehicle checkpoint. Speaking to WGRZ-TV, Mike Guenther said he saw a vehicle speeding toward the crossing from the U.S. side of the border when it swerved to avoid another car, crashed into a fence and exploded. “All of a sudden he went up in the air and then it was a ball of fire like 30 or 40 feet high,” Guenther told the station. “I never saw anything like it.” Ivan Vitalii, a Ukrainian visiting Niagara Falls, told The Niagara Gazette that he and a friend were near the bridge when they “heard something smash." “We saw fire and big, black smoke,” he told the newspaper. U.S. Attorney General Attorney General Merrick Garland and New York Gov. Kathy Hochul had been briefed on the situation, their offices said. The Niagara Falls Bridge Commission reported that all four of its crossings — the others are Lewiston, Whirlpool and Peace Bridge — were closed.