A vehicle explosion has reportedly closed the Rainbow Bridge that connects the US and Canada at Niagara Falls.

This is a breaking story. We'll have more for you as details come out.

Update 1:49 p.m. - From ABC News:

Ron Rienas, GM of the Buffalo and Fort Erie Public Bridge Authority, told ABC News all four Canada-U.S. bridges over the Niagara River have been closed out of an abundance of caution while the Rainbow Bridge investigation continues.

New York Gov. Kathy Hochul said, "At my direction, the New York State Police is actively working with the FBI Joint Terrorism Task Force to monitor all points of entry to New York. I am traveling to Buffalo to meet with law enforcement and emergency responders and will update New Yorkers when more information becomes available."

Update 1:59 p.m. - Fox News reports this was an "attempted terrorist attack" by two individuals in the vehicle (now deceased) who had explosives inside. One border agent has been injured. All government buildings have been evacuated.

Update 2:33 p.m. - ABC News reports the vehicle exploded at a secondary checkpoint on the bridge and that a suspicious briefcase was found at the scene.

Surveillance video showed the vehicle stopped at an initial security checkpoint, according to sources briefed on the investigation. The vehicle was then directed to a secondary security checkpoint, and at that point the vehicle sped up and crashed into the secondary screening location, sources said.

What triggered the initial security stop was not immediately clear. It is also not immediately clear what caused the explosion.

Investigators have found some sort of suitcase or briefcase on scene, sources told ABC News. They are treating it as a possible explosive device as a precaution and the bomb squad is handling the package.

Update 3:08 p.m. - This video shows the moment of the explosion. Police are reportedly looking for a second vehicle.

Update 4:30 p.m. - MSNBC has a purported video of the crash and is saying there 'is no indication whatsoever" that there were explosives or secondary explosives in the vehicle, but that the car burst into flames due to the high rate of speed when it hit the security checkpoint.

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