Rare snow and bitter cold blanket southern US states

A rare winter storm is gripping parts of the US deep south, closing highways and airports in Texas and prompting a first-ever blizzard warning in southwest Louisiana.

The Gulf Coast will see historic snowfall, the National Weather Service (NWS) said on Tuesday, with an inch of snow or more expected to fall per hour from eastern Texas through the western Florida Panhandle.

Temperatures are expected to fall well below January averages, and may surpass record lows stretching up from the coast into the Tennessee Valley.

Governors of several states, including Louisiana, Mississippi and Alabama, have declared states of emergency in response to the unusual cold.

The storm began in Texas on Monday evening, and was forecast to spread eastward through Wednesday morning along Interstate 10, a major highway in the region.

The extreme weather, part of a bitterly cold air mass that has descended on the south and eastern US, is forecast to linger over the next couple of days.

Around 40 million people, primarily across the southern US, were under some type of weather hazard, March Chenard, a meteorologist with the NWS, told BBC's partner CBS News. Another 170 million people from the Rockies to points eastward were under an extreme weather warning or cold weather advisory.

By Tuesday morning, snow was covering areas more known for hurricanes than blizzards, including the major cities of Houston and New Orleans.

Many school systems cancelled classes and three airports in Houston suspended flight operations.

The NWS cautioned that the rare storm could continue to cause "widespread" disruptions in both air and land travel for several days even after the snowfall stops.

More than 2,000 flights within the US were cancelled on Tuesday, and 13,000 more were delayed, according to online tracker Flight Aware.