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

A fiery pileup Friday at an Interstate 80 tunnel in southwestern Wyoming killed at least two people, seriously injured at least five others and shut down the highway. The crash involved an unknown number of trucks and other vehicles inside and outside the tunnel at Green River.

The National Transportation Safety Board said Saturday it had opened a safety investigation into the crash that took the lives of at least two people in a multi-vehicle crash inside a southwest Wyoming highway tunnel.