GREEN RIVER, Wyo. – Investigators in Wyoming began sifting through the wreckage inside a highway tunnel Saturday after smoke, hazardous chemicals and structural concerns prevented them from determining how many people may have died in the fiery pileup.

At least two people were killed and five others were seriously injured in Friday’s multivehicle crash, officials said. The crash took place in the westbound tunnel of Interstate 80 under Castle Rock, a snow-covered sandstone formation that looms over the town of Green River in the state’s southwest.

“It’s really going to be a long process just because of the magnitude of the incident and then being able to document everything that we need to make sure that our investigation is thorough,” said Maj. James Thomas of the Wyoming Highway Patrol.

Once officials are able to pull vehicles out, they will work with the county coroner, he said. Authorities still have yet to be able to count all the vehicles involved.

Photos of the scene Friday showed crumpled semitrailers outside the smoke-blackened mouth of the tunnel, which is about a quarter-mile long (400 meters).

Randy Ringstmeyer, a Wyoming Department of Transportation engineer, said there was extensive fire damage in the middle third of the westbound tunnel. The blaze damaged its concrete lining, causing loose concrete to fall and requiring first responders to avoid those areas.

Interstate traffic was being rerouted through Green River. Officials aimed to reopen the eastbound tunnel in three days so it can host two-way traffic while the westbound section remains closed. Engineers were unable to estimate when the westbound tunnel would reopen.

The National Transportation Safety Board said it has opened a safety investigation together with the highway patrol.