Harsh winter weather has swept across much of the United States, leaving scores of people dead, hundreds of thousands without electricity and threatening to decimate California's citrus crops.

At least 50 people have died in storm-related accidents since Friday, the majority in car accidents on icy roads, major US news media reported Wednesday.

A powerful storm that churned across the country from the southwestern states of New Mexico and Texas to far northeastern Maine starting on Friday is blamed for most of damage.

A separate icy snap in normally balmy California led California Governor Arnold Schwarzenegger to warn that the region's citrus fruit industry could be decimated.

Damage to the citrus industry alone "is close to a billion dollars," Schwarzenegger said.

California accounts for nearly a quarter of the US market for citrus fruits, according to state agricultural authorities. Avocados, green leafy vegetables, broccoli, strawberries and cauliflower also grow in the state and have been affected by the freeze.

Low temperatures also struck the US northwest, where cleanup crews in Portland, Oregon on Wednesday are focusing on de-icing major roadways after the area was hit with up to 13 centimeters (five inches) of snow on Tuesday.

Cars stuck in the snow were abandoned on Portland freeways, and transportation officials temporarily ordered all vehicles on the roads to use chains or traction tires.

City officials and forecasters had been expecting a light dusting and were unprepared for the heavy snowfall, local news media reported.

The sudden snowfall and slick roads also triggered a 30-car pileup on a major highway close to nearby Seattle on Tuesday.

Low temperatures will keep the snow and ice on the ground in the northwest at least until Friday, according to local forecasts.

The storm that covered much of the midwestern US was caused by a vast cold front that dropped temperatures by as much as 17 degrees C (30 degrees F) and brought wave after wave of freezing rain and sleet as it moved slowly eastward.

It weakened somewhat by early Wednesday, sparing the major East Coast cities of New York, Boston and Philadelphia from the worst of the ice and sleet.

"This is a big one, affecting all the way from New Mexico to Maine," said Dennis Feltgen, a spokesman for the National Weather Service.

Worst-affected areas were Oklahoma, where freezing rain left behind a sheet of ice, and Missouri, badly hit by sleet, he said.

"With the ice, the trees come down on the power lines, and in Oklahoma it's going to take the rest of the week to get all that restored," he said. "The lines are completely down. It's not like it's a transformer here and there -- it's the whole grid."

President George W. Bush declared an emergency in Oklahoma on Sunday, and Federal Emergency Management Agency workers were in the state handing out emergency supplies.

The Oklahoma Highway Patrol reported more than 300 road accidents in which at least 14 people were killed, including seven in a minivan crash Sunday.

The National Weather Service has issued storm warnings for central Texas, freeze warnings for California, Arizona and most of southern Texas, wind chill advisories stretching from New York to Maine, and flood warnings across central US from Louisiana, Kansas, Missouri, Indiana, Illinois and Ohio.

Forecasters said there had already been ice storms in western parts of New York state.

Bush also declared a state of emergency for Missouri -- including the city of St. Louis -- on Monday, freeing up federal funding for recovery efforts.

More than 300,000 people lost power in the state due to downed power lines, and a utility worker was injured, Missouri state officials said.

Some 51,000 homes and businesses lost power in upstate New York after a heavy layer of ice covered the area Monday, National Grid spokesman Alberto Bianchetti said Tuesday.

While power will be restored over the next days in storm-stricken areas, the California freeze "is something that's likely to affect farmers and consumers for months to come," said Dave Kranz, a spokesman for the California Farm Bureau Federation.

Kranz said it was still too early to put a dollar figure estimate on the losses but acknowledged damage was "widespread."

The freeze could be a costly blow to the industry, said Tim Chelling with the Western Growers Association, a trade group representing 2,500 farmers and produce shippers in California and Arizona.

A two-night 1998 area freeze resulted in 700 million dollars in crop losses, he said. "This is already a five-plus night event with another cold front predicted in 10 days," he said.