The storm was part of a massive system that brought snow, sleet and freezing rain to the southern Plains and was spreading across the Ohio Valley and to the Northeast.
The Southwest Power Pool, a group of utilities across 14 states, called for rolling outages because the supply of reserve energy had been exhausted.
Some utilities said they were starting blackouts, while others urged customers to reduce power usage.
Massive power outages across Houston included a facility storing 8,000 doses of Moderna vaccine, and health officials scrambled to find takers at the same time authorities were pleading for people to stay home.
State health officials said Texas, which was due to receive more than 400,000 additional vaccine doses this week, now does not expect deliveries to occur until at least Wednesday.
Most government offices and schools were closed for Presidents Day, and authorities pleaded with residents to stay home.
By mid morning, 3,000 flights had been canceled across the country, about 1,600 of them at Dallas/Fort Worth International and Bush Intercontinental airports in Texas.
The storm arrived over a three-day holiday weekend that has seen the most US air travel since the period around New Year’s.
US President Joe Biden also declared an emergency in Texas in a statement Sunday night.
The declaration is intended to add federal aid to state and local response efforts.