The stage-one emergency call is a public call for conservation. It can be declared after the reserve margin, a measure of surplus power, falls below 7 percent.

    State authorities predicted another power-demand record and the possibility of the most severe shortfall in five years because of the heat waves.

    The state said it may call the first stage-three emergency, which would lead to rolling blackouts, since 2001, when an industry restructuring and market manipulation by power traders led to widespread electricity shortages.

    California would declare a stage-three emergency and call for rolling blackouts when the reserve margin is less than 1.5 percent.

    A stage-two emergency comes at less than 5 percent and allows utilities to restrict power to some customers who have agreed to reduced supplies during emergencies in exchange for lower rates.

    California, with an economy twice the size of Russia's, has struggled to improve the reliability of its electricity system as a growing population spurs demand.

    "Conservation is now critical," said Yakout Mansour, the chief executive officer of the California Independent System Operator, which manages most of the state's electricity network.

    "We may have to go to stage three," he told a press conference.

    Rolling blackouts, if necessary, would likely be implemented for only a couple of hours during the late afternoon on Monday, Mansour said.

    The state forecasted that electricity demand would reach about52,000 megawatts, compared with a record 49,036 megawatts set at the end of last week.

    California is running commercials on 235 radio and TV stations calling for energy conservation, and state agencies are working to reduce power consumption by 25 percent at their facilities.

    "We remain confident that with the appropriate level of conservation, the lights will stay on," said Joe Desmond, undersecretary of energy affairs at the California Resources Agency, at the press conference. "The system as a whole is strained."

    The region was suffering one of the region's worst heat waves on record which have already caused the failure of transformers and fuses, resulting in blackouts. About 19,000 households and businesses are without power as of this morning, according to Edison, the region's major electricity supplier.

    Edision said Sunday that power failures had impacted 145,000customers.

    The heat waves was blamed for at least two deaths in northern California, including one that triggered a criminal investigation of a nursing home where air conditioning failed, causing the death of a patient.

    On Sunday in the Central Valley, temperatures soared to 113 degrees Fahrenheit (45 degrees Celsius) in Modesto, beating a record of 105degrees Fahrenheit set in 1960, while in Stockton, temperatures topped 115 degrees exceeding a record of 107, also set in 1960, the weather service reported.

    Edison, the electricity company, has been swamped by phone calls and could not respond immediately.

    "We are having a large number of people without service throughout the Southland, all related to the weather, the heat, the humidity," said Edison spokesman Steven Conroy. "We are seeing record consumption, record temperatures, and when operated at high use continually, there is a chance of equipment failure, and that's what's happening today."

    Monday was the 19th consecutive day that temperatures reached triple digits in parts of the Los Angeles Basin.

    The National Weather Service has issued yet another warning of "dangerous heat and humidity" across most of Southern California, triggered by moisture from monsoonal conditions combined with an extra-strong ridge of high pressure that refused to budge.

    Consumption is surpassing previous forecasts made by the system operator, which previously this year said that demand would peak at about 46,000 megawatts under "most likely conditions" and about 49,000 megawatts under adverse conditions. One megawatt is enough for about 800 U.S. homes.

    The heat and humidity led the weather service in Los Angeles to issue an excessive heat warning for southwestern California until at least 7 p.m. local time, indicating that a prolonged period of dangerously high temperatures will occur.

    The state's system operator first called for conservation during the current heat wave on July 14. California set records for power demand on July 17 and July 21, breaking the high established a year ago. The state endured its first stage 1 emergency of the year two days ago after a power plant unexpectedly shut down. Enditem