The low visibility on Interstate 40 near Flagstaff caused about 20 collisions, which occurred over a stretch of highway at least 4 miles long around noon, Flagstaff Fire Department Chief Mark Wilson said.
He described the wrecks as clumps of vehicles piled on top of each other, involving cars, trucks and semis.
"The magnitude of it was pretty severe," Wilson said. "We had a whiteout scene with the snow, and obviously a single-vehicle accident caused multiple-vehicle accidents, which continued to pile up due to the low visibility."
While the state public safety department said three people were killed, Wilson said there were two. Neither could immediately clear up the confusion.
Wilson said 15 people had to be extracted from their vehicles with hydraulic equipment or hand tools.
Flagstaff Medical Center spokeswoman Starla Addair said the hospital received 53 patients, at least 10 of whom needed to be admitted. She did not know their condition or whether any of the 53 patients had been released.
Red Cross volunteer Gene Munger said about 40 people involved in the wrecks were at a middle school shelter Sunday evening deciding whether to spend the night there on cots or find a hotel.
He said those he talked to described the scene of the accidents as complete chaos. "They're pretty shook up right now," he said.
National Weather Service meteorologist Clair Ketchum said whiteout conditions occurred off-and-on Sunday afternoon in the Flagstaff area and could occur overnight as a storm rolls across the state.
Ketchum said 3.8 inches of snow fell by 5 p.m. Sunday near where the collisions occurred.