HOUSTON, United States 

A rare winter storm barreled into the US state of Texas early Tuesday, plunging the region into a deep freeze, with Houston receiving 4 inches (10.16 centimeters) of snow and up to 6 inches (15.24 cm) forecast for surrounding areas.

Both international airports in Houston canceled flights due to the hazardous conditions. In addition, schools in the area canceled classes, most businesses have shut down for the next two days and Houston closed all offices on Tuesday and Wednesday due to the dangerous weather, with the exception of emergency services.

"Essential services, first responders, the health department, our mental service center (and) warming centers will be open 24 hours into sometime Thursday," said Houston Mayor John Whitmire in an interview with Houston Public Media.

Harris County, which is the largest populated county in Texas, and includes Houston, opened up 23 warming centers for those in need of a safe place to stay for the duration of the life-threatening conditions.

"We did see around 1,100 people across the 23 warming centers last night," Harris County Judge Lina Hidalgo told Houston Public Media.

A combination of freezing rain, sleet, snow and icy conditions forced law enforcement officials to shut down major interstates, highways and roadways throughout the state, including the Galveston area, 60 miles (96.56 kilometers) south of Houston.

"Bridges and Overpasses are iced over, crews are continuously treating where necessary," said the Galveston County Office of Emergency Management in an alert.

"Avoid driving today, conditions on the roadways are dangerous," it said. "Expect a Hard Freeze tonight."

Nearly 40 million people across mostly the southern US are under some type of winter weather hazard, including more than 21 million who are under a winter storm warning in Texas, Louisiana, Mississippi, Alabama, Georgia and Florida, according to the National Weather Service (NWS). The first-ever blizzard warning was issued in Louisiana with winds over 35 miles per hour and blowing snow expected to cause reduced visibility.

The NWS said about 170 million people from Colorado all the way to the East Coast were under an extreme weather warning or cold weather advisory.

Continued snow, sleet, freezing rain and icy conditions are expected overnight in the Houston area. The Harris County Office of Homeland Security and Emergency Management is warning residents to stay inside until the storm passes.

"STAY OFF THE ROADWAYS!!! The roads are a DANGEROUS place right now and conditions will continue to worsen tonight and into tomorrow morning," it said. "For your safety and others, please stay home and off the roads."​​​​​​​