A car traveling at high speed crashed into a checkpoint barrier and exploded into flames at the United States side of a border crossing to Canada on Wednesday, killing its two occupants.

The crash at the Rainbow Bridge crossing near Niagara Falls, New York also triggered border closures and sparked a massive security alert on the eve of the US Thanksgiving holiday.

New York Governor Kathy Hochul confirmed the two fatalities in the blast at the checkpoint 640 kilometers northwest of New York City and said nothing pointed to a "terrorist" attack.

"There is no evidence at this time that this was terrorist activity," Hochul told a briefing.

While the two victims' identities were not yet public, she suggested their vehicle may have been from western New York state.

Nothing was left of the vehicle which Hochul said was incinerated except for the engine.

Hochul said that crash debris was spread across as many as 14 of the lanes at the crossing following the incident.

Authorities on both sides of the border activated emergency responses and images showed access roads to the crossing swarming with emergency service workers and vehicles.

On the US side, Niagara Falls State Park, which attracts millions of visitors every year, was closed until further notice according to the parks service.

Multiple witnesses reported hearing a loud explosion and seeing a large cloud of smoke near the inspection station.

"We've seen this car coming down towards the border and he was flying — over 100 miles an hour," Mike Guenther, a Canadian visiting the United States, told CBS News.

The car then swerved and "hit the fence, went flying up into the air," he said. "He went up into the air and we just seen the fireball and that's all we could see. It was just covered in smoke everywhere."

Ivan Vitalii, a visitor from Ukraine, told the Niagara Gazette he and a friend were at a nearby convenience store on the US side when they saw a car exit a parking lot and travel toward the bridge.