PHOENIX - Dozens of vehicles collided in heavy, blinding snow on a northern Arizona interstate Sunday, killing at least two people, critically injuring 11 others and forcing police to close the highway for 20 miles in both directions.

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. He said 52 patients, 11 of them critical, were taken to Flagstaff Medical Center. He said four were in surgery Sunday evening.

Hospital spokeswoman Starla Addair said it was too early to comment on the status of the patients, but said the hospital was handling the amount of patients well.

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.