A border crossing between the U.S. and Canada has been closed after a vehicle exploded at a checkpoint on a bridge in Niagara Falls, authorities said.

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.

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.

The FBI’s field office in Buffalo said in a statement that it was investigating the explosion.

Gov. Kathy Hochul said she had been briefed on the incident and was “closely monitoring the situation.”

The Niagara Falls Bridge Commission reported that all four of its crossings — the others are Lewiston, Whirlpool and Peace Bridge — were closed.

Further information wasn’t immediately available on the cause of the explosion.