WACO, Texas — A fiery chain collision involving four semitrailer rigs and two passenger vehicles in Waco in Central Texas has killed at least three people and closed Interstate 35 northbound for hours.

The crash happened about 2 p.m. Tuesday on I-35 at Spur 396. Witnesses say a semitrailer and two cars were slowing when another semi slammed into the cars from behind with all erupting in explosions and flames. They saw two people trying to crawl from the wreckage when they exploded before they reached safety.

Waco police Sgt. W. Patrick Swanton says vehicles were mangled so severely that it was unclear if all occupants are accounted for.

I-35 was closed for two hours when southbound lanes were reopened. Swanton says northbound lanes are expected to remain closed until early Wednesday.