US President Barack Obama is due to visit the southern state of Alabama to receive a firsthand account of the trail of destruction left by tornadoes, which killed nearly 300 people

US President Barack Obama is due to visit the southern state of Alabama to receive a firsthand account of the trail of destruction left by tornadoes, which killed nearly 300 people.

The White House said that Obama will be there on Friday. Earlier, Obama received an update on the disaster from Janet Napolitano, the homeland security chief, and other officials as people in seven affected states come to terms with scenes of utter devastation.

Becoming the deadliest storms in the US since Hurricane Katrina in 2005, the violent weather left thousands of people homeless and millions more with power outages.

Obama declared state of emergency in Alabama, the hardest-hit state. He also vowed to mobilise the federal government's resources to help the storms-ravaged region.

"While we may not know the extent of the damage for days, we will continue to monitor these severe storms across the country and stand ready to continue to help the people of Alabama and all citizens affected by these storms," Obama said in a statement.

Obama is to stop in Alabama on his way to Cape Canaveral, Florida, to view the launch of the space shuttle Endeavour. He will meet the Alabama governor as well as local officials.

The clusters of powerful tornadoes - more than 160 in total - combined with storms cut a swathe of destruction heading from west to east over several days.

In preliminary estimates, other state officials reported 32 killed in Mississippi, 30 in Tennessee, 11 in Arkansas, 14 in Georgia, eight in Virginia and two in Louisiana.

Some of the worst devastation occurred on Wednesday in Alabama, where a massive 1.6km tornado slammed into the town of Tuscaloosa, home to 95,000 people in the west-central part, killing at least 37 people including some students.