A tractor-trailer hauling a hazardous chemical on Interstate 81 caught fire Thursday afternoon, blocking the highway's northbound lanes, forcing the evacuation of surrounding homes and prompting an hours-long effort to put the fire out.

The incident started about 5:30 p.m. when the northbound tractor-trailer's brakes caught fire between the Interstate 581 exit and the Plantation Road exit, according to Roanoke County authorities. The driver pulled over and called 911, said Joey Stump, a division chief with the Roanoke County Fire and Rescue Department.

The driver was not injured in the incident.

The tractor-trailer was carrying sodium hydrosulphite, Stump said, a hazardous chemical that produces fumes when in contact with water.

Firefighters evacuated about 80 homes within a half-mile of the incident Thursday night before entering the burning trailer, Stump said.

"They're making access into the trailer now," he said after a short press briefing about 11 p.m. Thursday.

Most of those evacuated were to spend the night with friends and relatives but about 10 people took shelter in the Salem Civic Center.

The incident tied up traffic for hours in the northbound lanes of the interstate with drivers rerouted to Peters Creek Road in Roanoke.

"We really hope that the roadway will open in the morning," Stump said. "At this point we don't have a guarantee."