Tornadoes and storms in the south-eastern United States have killed at least 215 people, officials say.
In Alabama, the worst-hit state, 131 have died in recent days - including 15 killed by a tornado that devastated the city of Tuscaloosa.
Deaths and widespread devastation are also reported in Tennessee, Mississippi, Georgia and Virginia.
A state of emergency has been declared in seven states, and federal aid money is being sent to Alabama.
In Alabama, as many as one million people were without power on Thursday morning, as emergency workers and 2,000 soldiers scoured the wreckage for survivors.
Governor Robert Bentley said he expected the death toll to rise as more bodies were discovered in the rubble.
"We still have a number of people that are missing this morning, and we have all ground and air assets that are up in those areas trying to search for those missing individuals," he told reporters.
Mr Bentley said Alabama residents are accustomed to tornados and had taken precautions, but "in highly populated areas, it just makes it very difficult to move everyone out when a tornado comes through that's a mile wide."
The US National Weather Service has preliminary reports of nearly 300 tornadoes since the storm began on Friday, more than 150 on Wednesday alone.
One meteorologist described the tornado that devastated Tuscaloosa as possibly the "worst in Alabama's history". (read more)