At least three people were killed and millions more were stuck in homes without electricity as a deadly winter storm continued to batter the U.S., delivering heavy snow and icy temperatures so low they broke records in many places, CNN and other news reported on Tuesday.

In Texas, many suffered from extreme cold temperatures in the dark, Monday. Most of the city of Austin has no electricity and some resorted to sleeping in their cars while running the engine for warmth.

The unusual winter storms left people freezing in dangerous conditions across swathes of the southern U.S., the National Weather Service said.

The cold weather slammed the Midwest Monday, shutting down Houston's airport and cancelling more than 3,800 flights nationwide.

The deep freeze across the country dealt a heavy blow on the energy industry in Texas, the U.S.' biggest crude-producing state, halting oil refineries and forcing restrictions from natural gas and crude pipeline operators, Reuters reported.

Texas Governor Greg Abbott ordered the deployment of the National Guard to check on his constituents and help set up emergency warming facilities.

At least 13 people have died in weather-related vehicular mishaps since cold temperatures gripped the country.

Nine were killed in three road accidents in Texas Thursday, one person died in a collision in Oklahoma Sunday and three people perished in Kentucky.

In Lafayette, Louisiana, a 50-year-old man was killed after slipping and hitting his head on ice, local officials said Monday.

"For those without power, I know it is cold," Houston Mayor Sylvester Turner tweeted. "The mayor is in the same position, but we will get through this together."

Texas has borne the brunt of the winter pummeling. Harris County, home to Houston, officials warned its 4 million residents to stay indoors because the icy weather will be around for a while.

In a statement Sunday night, U.S. President Joe Biden declared a state of emergency in Texas and ordered federal assistance to help state and local response efforts.

More than 70% of the United States was blanketed in record-thick snow as of Monday afternoon, weather officials said.

More than 50 million people could see temperatures drop below zero in the next several days, the Capital Weather Gang reported.