A minivan carrying 12 people skidded off an icy highway early Sunday and slammed into an oncoming tractor-trailer, killing seven people after seven other deaths were blamed on the weather, the Oklahoma Highway Patrol said.

The eastbound van slid through the center median and struck a westbound tractor-trailer on Interstate 40 around 3:50 a.m., trooper Kera Philippi said. Five of the van's occupants were taken to a hospital, Philippi said.

The identities of the woman and six men who were killed were not immediately released. Philippi said all the van's occupants were adult residents of Mexico. "The medical examiner has made positive identification of some of them, but they're having to use interpreters to locate next of kin," Philippi said.

All seven victims were thrown or partially thrown from the minivan and apparently were not wearing seat belts, trooper Chris Laufer said. They were pronounced dead at the scene, he said.

At the time of the crash, about 110 miles west of Oklahoma City, freezing rain was falling and visibility was limited, according to the National Weather Service. A powerful winter storm had coated roads and highways with ice and sleet.

The crippling winter storm lashed the central part of the nation with a blast of freezing rain, sleet and snow Saturday, causing widespread power outages and tying up highways and airports.

The storm was expected to continue through the weekend, laying down a coat of ice and snow from Texas to Illinois, where an ice storm warning was in effect through Monday morning.

"We're in the middle of this storm," said Joe Pedigo, meteorologist for the National Weather Service in St. Louis. "Friday was the first of three waves."

Farther west, frigid arctic air reached as far south as southern and central California, where plunging temperatures prompted worry about the homeless and crops.

The storm in the Midwest had been blamed for at least seven deaths and brought Amtrak service in Missouri to a halt on Saturday. Trees and other debris knocked down by the weight of ice blocked tracks at several locations between St. Louis and Kansas City.

About 90,000 homes and businesses had no electricity Saturday in Missouri, mostly in the St. Louis area, while 6,000 customers were in the dark in Illinois.

"We have hundreds of crews. We kept them working all night long," said Susan Gallagher, a spokeswoman for the utility Ameren. "Like everyone, we don't know what the extent of damage will be with the arrival of more ice."

Between 60,000 and 70,000 customers were without power in Springfield, Mo., Saturday, plus an unknown number of homes and businesses in surrounding towns, said Jenny Fillmer Edwards, spokeswoman for the Springfield-Greene County Office of Emergency Management.

Roads in southwest Missouri began freezing after sunset. Two shelters in Springfield filled Saturday and emergency officials planned to open one more. There were also three shelters for people with special needs and medical conditions.

Missouri Gov. Matt Blunt and Texas Gov. Rick Perry activated their National Guard members on Saturday. Blunt, who also declared a state of emergency, said the worst wave may come Sunday.

In San Marcos, Texas, a tornado damaged at least 13 homes, several businesses and the police headquarters. Fallen power lines blocked a section of Interstate 35 until crews could remove them, said Melissa Millecam, communications manager for the city, 30 miles south of Austin.

"It's a good bit of damage," she said. "It's still stormy and we've got power outages in different places."

More than 6 inches of rain fell in places across central Texas, causing local flooding. Water also blocked three highways in southeastern Oklahoma, the Department of Transportation reported.

About 300 flights were canceled Saturday at Dallas-Fort Worth International Airport, spokesman David Magana said. Cancellations also were reported in St. Louis, Kansas City, Oklahoma City and Tulsa.

In Oklahoma, about 92,450 customers were without power early Saturday, the Oklahoma Department of Emergency Management said.

More rain, freezing rain and snow was expected from northwest Oklahoma all the way to Wisconsin on Sunday, Pedigo said.

In Nevada, temperatures plunged as much as minus 28 in the northern part of the state, filling homeless shelters to capacity and prompting ranchers to use axes to break ice in troughs so cattle could drink, authorities said.

In California's San Joaquin Valley, where much of the state's nearly $1 billion citrus crop is grown, temperatures dropped into the teens overnight Friday. Growers burned fires, sprayed warm irrigation water and ran giant fans to keep cold air away from their oranges, lemons and tangerines.

A.J. Yates, California's agriculture undersecretary, said the citrus industry could be substantially damaged if the temperature stays below 25 degrees for six hours or longer. Citrus growers said it was too soon to evaluate the damage.

"Overall I don't think it was a catastrophe last night," grower Ron Turner, 52, of Exeter, said Saturday. "But how this thing plays out in the next few days is going to be the key."