Officials with the Colorado Department of Transportation sent out a warning to Denver-area drivers on Thursday afternoon to avoid heading up to the high country due to a fatal crash on Interstate 70. Westbound I-70 reopened after 5 p.m., about 4 hours after the collision, and there were still big backups at 5:30 p.m.

The crash was in the westbound lanes right before the Eisenhower Tunnel.  

A person and a dog were killed in the crash, which involved a semi truck and a pickup truck hauling a trailer. It happened just after 1 p.m. in the westbound lanes and a large fire with heavy smoke resulted from the collision.

The person and the dog were in the pickup truck. The person's identity has not been released. The semi driver wasn't hurt.

The cause of the crash is under investigation.

"Motorists are strongly encouraged to avoid travel from Denver to the high country via Interstate 70 and US Highway 285 until this evening," officials from CDOT wrote in an afternoon news release.

Colorado State Patrol said drivers who attempt to head up to the mountains in the afternoon could "expect extreme congestion and heat."

The eastbound lanes were closed for a short time after the crash. They reopened about an hour after the crash. Drivers heading eastbound were also warned to expect heavy holiday traffic.