Part of Highway 6 has reopened after a fiery three-car crash killed two men in Mt. Hope, near Hamilton, Tuesday morning.

Ontario Provincial Police reopened Highway 6 around 12:30 p.m., after closing a stretch of road at Chippewa Road West, south of Airport Road, while investigating how the crash happened.

The highway remained closed all morning as OPP investigators worked to piece together what happened. (Tony Smyth/CBC)

It happened just before 7 a.m., said OPP Sgt. Kerry Schmidt, when a Volvo crossed into the oncoming lanes of Highway 6. Police originally thought the SUV has crossed over into the opposing lanes.

Then the Volvo caught fire. Hamilton fire spokesperson Claudio Mostacci said when firefighters got to the scene, one vehicle was fully engulfed in flames. He couldn't say if anyone was still inside.

Another car then plowed into the two vehicles, sending all three spinning sideways, Schmidt said.

The 53-year-old driver of the SUV was pronounced dead at the scene, while the 18-year-old who was driving the Volvo was rushed to hospital in critical condition, where he then died.

The driver and passenger of the third vehicle were taken to hospital with minor injuries.

It took fire crews about 15 minutes to douse the car fire, Mostacci said. "You try to put it out before it gets to the gas tank," he said.

Schmidt told CBC News that the roads in the area are wet and it's snowing. "But you can still see the highway lines quite clearly," he said. "The roads weren't a huge factor."

Investigators are now trying to figure out what caused the crash. No cause has been determined. Speed and alcohol have not been ruled out.

Police are working on notifying the families of the crash victims, and expect to release their names later Tuesday or early Wednesday, Schmidt said.

An Ornge air helicopter was originally called in because of the crash, but then cancelled.