Obama toured smashed homes and met survivors on a visit to the worst-hit state, Alabama. It was one of seven southern states mauled by recent tornadoes and storms which have caused insured losses of between US$2 billion and US$5 billion, according to one catastrophe risk modeler's estimate.

"We are going to do everything we can to help these communities rebuild," Obama told reporters in Tuscaloosa, a university city in Alabama that was devastated by the tornadoes.

"I have never seen devastation like this. It is heartbreaking," said Obama, accompanied by his wife Michelle and Alabama Governor Robert Bentley. "This is something I don't think anyone has seen before."

Emergency officials in Alabama again raised the death toll from the tornadoes in that state to 238. Bentley also said 1,700 people were injured.

At least 101 more deaths were reported across Mississippi, Tennessee, Arkansas, Georgia, Virginia and Louisiana.