PHOENIX — Multiple collisions involving 69 vehicles jammed westbound Interstate 10 on Saturday evening in downtown Phoenix.

Seven people were taken to area hospitals, two in serious condition. Phoenix Fire officials say they medically evaluated at least 40 people at the scene.

Arizona Department of Public Safety officials attributed the crashes to the thunderstorms that swept through the Phoenix area around 6 p.m.

"The rain came down hard and fast," said Sgt. Robert Bailey, a DPS spokesman.

One collision alone involved 35 vehicles and spanned more than 2 and one-half miles, according to Phoenix Fire officials.

Bailey said "dozens and dozens" of calls to 911 were received in a 15 minute span, starting around 6:15 p.m.

"This is all definitely weather related," he said. "It caught a lot of drivers by surprise."

Bailey compared the collisions to frequent dust storm crashes: "People are driving freeway speeds without slowing down. It's like a big chain reaction."

Still, many were surprised that there weren't more serious injuries on the stretch of freeway where the speed limit is 65 mph.

Phoenix Fire spokesman Captain Jonathan Jacobs said he suspects motorists had slowed down because of the rain. Phoenix fire had about 100 firefighters working the scene.

Multiple tow trucks hauled away disabled vehicles as a city bus drove up and down the closed section of the freeway, providing shelter and air conditioning to the victims, Jacobs said. About half of the vehicles involved could be driven away.