A huge winter storm sweeping across the southern US has killed at least 21 people and left millions without power.

There have been widespread blackouts in Texas, where the energy grid was overwhelmed by a surge in demand.

Millions of people in the state, which rarely experiences such low temperatures, have been struggling to cope with the lack of power and frigid conditions.

The extreme weather is forecast to continue until the weekend.

Deaths attributed to the storm have been recorded in Texas, Louisiana, Kentucky, North Carolina and Missouri.