Border crossings between Canada and the US have been closed after a vehicle exploded on a bridge between the two countries, reportedly killing two people.

The explosion happened on Rainbow Bridge, near the Niagara Falls in Canada, which borders western New York State on Thursday morning (AEDT).

Two occupants of the vehicle are reportedly dead and a border official injured, according to the Fox News Channel.

Official details of the incident were murky.

The Niagara Gazette newspaper, citing law enforcement sources, said the car sped onto the bridge plaza, went through a fence separating the inbound lanes from the outbound lanes, and toward the inspection lanes, where it exploded.

Media reports are conflicting as to whether the vehicle was driving from Canada to the US or vice versa.

The FBI said the situation was “fluid”, as a large contingency of law enforcement officers descended on the scene.

Debris inside the customs plaza at the Rainbow Bridge border crossing. Photo: AAP (The Buffalo News)

The Rainbow Bridge and the three other border crossings between western New York and Canada – the Peace Bridge, the Lewiston-Queenston Bridge and the Whirlpool Bridge – were shut indefinitely as a precaution, the New York governor’s office said.

New York Governor Kathy Hocul said authorities were “closely monitoring” the situation and state agencies were on site.

“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.”

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The three US-Canada crossings along the Niagara River separating southern Ontario and New York state are among the busiest in the world.

Security measures were escalated at airports and railways in the region managed by the Niagara-Frontier Transit Authority, the governor’s office said.

“This is obviously a very serious situation. The government of Canada is taking this situation extremely seriously,” Public Safety Minister Dominic LeBlanc said in Ottawa.

“We are in close contact with American authorities. I will be speaking with the US homeland security secretary shortly.”

The explosion was being investigated by agents from the FBI field office in Buffalo, New York, the agency in a statement on X.

“The FBI is coordinating with our local, state and federal law enforcement partners in this investigation,” the FBI statement said.

“As this situation is very fluid, that’s all we can say at this time.”

This is a developing story

-with AAP