FRESNO, Calif. (AP) -- California citrus growers are sweating a hard freeze that has blanketed the nation's largest fresh-fruit market in the midst of harvest.

The National Weather Service says temperatures dropped to as low as 19 degrees in some regions early Tuesday. It forced orange farmers to fire up wind machines and flood groves with water to keep bitter cold air from settling.

Oranges begin to suffer at about 28 degrees.

Officials with the Fresno County Agricultural Commissioner's Office are sampling fruit from the coldest regions looking for signs of freeze damage.

Deputy Commissioner Fred Rinder says officials will examine fruit Friday in affected areas to see if the freezing burst the tiny juice-storing cells inside the oranges that leads to dryness.

The commissioner can withhold damaged fields from the fresh-fruit market.