.
"There was an explosion just by the tall building you go in. My own van was parked so close to the car that exploded," one man, who had crossed over the bridge with his family, told the outlet.
"When the explosion happened, we heard it like a loud boom.
"I heard it, but I didn't think it was something serious. Someone said, 'Oh my god, the car exploded.'
"We all went to watch. Then the US border and customs officials came out of their glass room and then I grabbed my phone, said I need to film this before they start moving us away from here."
"The FBI Buffalo Field Office is investigating a vehicle explosion at the Rainbow Bridge, a border crossing between the US and Canada in Niagara Falls," the FBI field office said in a statement.
"The FBI is coordinating with our local, state, and federal law enforcement partners in this investigation.
"As this situation is very fluid, that's all we can say at this time," the bureau said.
Canadian Public Safety Minister Dominic LeBlanc told reporters on Wednesday that his team is taking the incident very seriously.
"This is obviously a very serious situation,“ LeBlanc said.
“We’re taking this circumstance very seriously, but to speculate on the origin of this particular circumstance – the reasons why this may have happened – until we have more accurate information is simply not responsible."
The two other bridges that connect the US and Canada in western New York, Peace Bridge, and Lewiston-Queenston, have since been reopened to drivers.
President has been briefed on the explosion and is monitoring any developments, according to .
Photos from the scene show debris scattered across the ground Credit: Twitter