California Governor Arnold Schwarzenegger warned that losses to the region's citrus fruit industry could reach one billion dollars as crops froze under an arctic cold spell.

In a letter to the US Department of Agriculture in Washington, Schwarzenegger said California's fruit industry was facing its worst ever crisis because of prolonged low temperatures that have chilled the state.

"The financial losses to the agricultural industry will likely reach one billion dollars," Schwarzenegger said in the letter released by his office, which urged authorities to expedite any requests for assistance made on behalf of California's fruit growers.

Schwarzenegger has declared a state of emergency in California, which has been gripped by unusually cold weather since last week.

California accounts for nearly a quarter of the US market for citrus fruits, according to figures from state agricultural authorities, making it the biggest producer of fruit in the nation.

A spokesman for the California Farm Bureau Federation, the state's biggest agricultural trade grouping with 92,000 members, said earlier the extent of the damage from the freeze was still being measured.

"We know there's been damage and we expect it's been significant," said CFB spokesman Dave Kranz. "But we won't know for a few days just how much damage has occurred."

Kranz said orange and lemon groves were expected to have suffered damage along with avocados, strawberries and vegetables.

"Essentially any fruit that was on a tree or any vegetable that was above ground may have been affected," Kranz said.

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

"The folks we've talked to say it's way too early to make that sort of a prediction," Kranz said when asked to comment on reports that up to 70 percent of the crop could be lost.

"The freeze in 1998 was severe but there were pockets of fruit that survived. That's the expectation this year. There are citrus groves that will have come through okay but there is also widespread damage."

Farmers had attempted to combat the freeze by pumping water into groves in order to raise the ground temperature and using giant blowers to circulate warm air around fruit, Franz said.

"Those techniques can increase the temperature in a grove from anywhere between two to five degrees," he told AFP. "Sometimes that can be the margin between losing a crop and saving it.

"But if temperatures drop into the mid-20s (Fahrenheit, minus six Celsius) for eight or nine hours, in many cases it trumps whatever frost protection measures the farmers take. If it stays that cold for that long, there is going to be damage."