Investigators are trying to figure out what caused a fiery highway crash that killed a 43-year-old woman in Barrie early Wednesday morning.

The woman died when the Jeep Wrangler she was driving crashed into a bridge support and then rolled several times before it caught fire, said Sgt. Dave Woodford, an Ontario Provincial Police spokesman.

The crash occurred in Highway 400’s northbound lanes at Dunlop Street shortly before 1:30 a.m.

Passersby pulled the woman, who was partially ejected, out of the vehicle before it exploded, but she was pronounced dead in hospital.

Because of a police investigation at the scene, northbound Highway 400 was closed between Dunlop and Bayfield streets in Barrie until 8 a.m.

Police do not know why the woman's vehicle veered into the bridge support, but it does not appear a second vehicle was involved in the crash, Woodford told CP24 reporter Cam Woolley.

Officers are hoping to speak to people who witnessed the crash or saw the woman before she was killed.

Anyone with information is asked to call OPP.

With files from CP24 reporter Cam Woolley