Four people are dead and two others are in critical condition after a chain-reaction crash involving 12 vehicles on an Arizona highway Saturday afternoon, possibly caused by blowing dust, authorities said.

The crash, which happened on Interstate 10, more than 50 miles west of Phoenix, involved six commercial motor vehicles, four passenger vehicles, a van and a recreational vehicle towing a trailer, according to the Arizona Department of Public Safety.

Investigators with the Arizona Highway Patrol believe there was an initial crash followed by several others. Several vehicles caught fire.

On Sunday, the Department of Public Safety said that two people remained in critical condition and one person was receiving precautionary care at a hospital. Five other people were treated and discharged. The names of the victims were not immediately made public.

On Saturday, a large section of southern Arizona, a desert region, was under wind and blowing dust advisories, but the area where the crash happened was not under a blowing dust advisory, said Mark O’Malley, a forecaster with the National Weather Service in Phoenix.

Wind speeds in the area of the crash were about 20 to 25 mph at the time, he said, and conditions were otherwise clear.