A vehicle has exploded on a bridge in Niagara Falls, situated between the US and Canada.
Two people so far are understood to have died as a result of the blast.
The reported victims are two men.
It is understood that the event is being investigated as an attempted terror attack.
WATCH NOW: Rainbow Bridge explosion
The FBI has described the situation on Rainbow Bridge as "very fluid".
All four land crossings connecting the two countries have been closed until more is known about the cause of the blast.
"As this situation is fluid, this is all we can say at this time," the FBI said in a statement.
Buffalo Airport has halted all international flights.
The bridge was closed at around 11.51am following the incident, according to the Niagara International Transportation Technology Coalition.
The City of Niagara Falls says the explosion came from a car that was driving from Canada to the US.
New York Governor Kathy Hochul also confirmed there had been an incident.
"State agencies are on site and ready to assist," she posted on social media.
"I am traveling to Buffalo to meet with law enforcement and emergency responders and will update New Yorkers when more information becomes available," she added.
The Niagara Frontier Transportation Authority said it would be increasing security.
WATCH NOW: CCTV footage of the moment the explosion begins
The bridge was closed at around 11.51am following the inciden
Those traveling through the Buffalo Niagara International Airport should expect additional screenings and vehicles coming into the airport will undergo security checks.
The explosion took place one day before the Thanksgiving holiday in the US, one of the busiest travel days of the year.
Rainbow Bridge connects Ontario with New York.
It links the cities of Niagara Falls, US with Niagara Falls, Canada.
The Peace Bridge, Lewiston-Queenston Bridge, Whirlpool Bridge, and Rainbow Bridge have also been closed in both directions, officials say.
