(Reuters) – A rare deep freeze in Texas that raised demand for power forced the U.S. state’s electric grid operator on Monday to impose rotating blackouts that left more than 2 million customers without power.

The PowerOutage.us website – an ongoing project created to track power outages – said 2,629,684 customers were experiencing outages at 9:44 a.m. ET (1444 GMT).

President Joe Biden declared an emergency on Monday, unlocking federal assistance to Texas, where temperatures on Monday ranged from minus 8 to 21 degrees Fahrenheit (minus 22 to minus 6 Celsius).

Apart from Texas, much of the United States from the Pacific Northwest through the Great Plains and into the mid-Atlantic states was in the grip of bone-chilling weather over the three-day Presidents Day holiday weekend.

The Electric Reliability Council of Texas (ERCOT) sought to cut power use in response to a winter record of 69,150 MW on Sunday evening, more than 3,200 MW higher than the previous winter peak in January 2018.

About 10,500 MW of customer load was shed at the highest point, enough power to serve approximately two million homes, it said, adding that extreme weather caused many generating units across fuel types to trip offline and become unavailable.

As of early Monday, it said over 30,000 MW of generation had been forced off the system, and rotating outages would likely last throughout the morning and could be initiated until the weather emergency ended.

“Every grid operator and every electric company is fighting to restore power right now,” ERCOT President and CEO Bill Magness said in a statement.

The storms knocked out nearly half the state’s wind power generation capacity on Sunday. Wind generation ranks as the second-largest source of electricity in Texas, accounting for 23% of state power supplies, ERCOT estimates.

Of the 25,000-plus megawatts of wind power capacity normally available in Texas, 12,000 megawatts were out of service on Sunday morning, an ERCOT spokeswoman said.

A level three emergency notice was issued by the regulator, urging customers to limit power usage and prevent an uncontrolled systemwide outage.

The National Weather Service said an Arctic air mass had spread southwards, well beyond areas accustomed to freezing weather, with winter storm warnings posted for most of the Gulf Coast region, Oklahoma and Missouri.

The spot price of electricity on the Texas power grid spiked more than 10,000% on Monday. [NGA/]

(Reporting by Aishwarya Nair and Diptendu Lahiri in Bengaluru; Editing by Bernadette Baum, David Goodman and Howard Goller)