The crashes - described by authorities as the most in a single Phoenix area in recent memory - began about 6:30 p.m., with many drivers going too fast or not leaving enough distance between cars for the slippery conditions, Department of Public Safety spokesman Bob Bailey said.
"The storm hit hard, hit fast, and caught a lot of drivers by surprise," he said. "The collisions began in the far right side of the roadway near the 7th Street exit ramp and this thing kind of perpetuated itself, enveloping the whole roadway."
CBS Affiliate KPHO reports seven people with serious injuries, none life-threatening, were taken to area hospitals, according to the Phoenix Fire Dept. Fire personnel also treated 30 to 40 people who had minor injuries at the scene.
None of the injuries was life threatening and most were fairly minor, Bailey said.
A five-mile stretch of westbound Interstate 10 was closed for about 3½ hours, reopening about 10 p.m. PDT. DPS said the roadway was blocked off at Washington Street near downtown Phoenix and several key onramps are also closed.
Bailey said at least half the vehicles in the crashes had to be towed away, accounting for the lengthy closure of the westbound lanes. Eastbound traffic on I-10 wasn't affected.
Dozens of people involved in the accidents remained on the interstate for hours after the accidents, Phoenix Fire Department spokesman Jonathan Jacobs said.
Authorities handed out snacks and water and brought in air conditioned city buses for them to relax in until arrangements were made to transport them home, he said.
Summer monsoon storms in the Phoenix area desert can bring heavy deluges with little warning, often causing localized flooding.