US President Barack Obama surveys damage caused by devastating severe storms and tornadoes in the Tuscaloosa, Alabama, April 29, 2011. [Photo/Agencies]

PLEASANT GROVE, Alabama - The US government ramped up efforts on Saturday to help thousands of homeless victims of the country's second deadliest recorded tornado outbreak, which killed at least 350 people.

President Barack Obama, who surveyed the tornado destruction in the worst-hit state of Alabama on Friday and called it "heartbreaking," was sending top officials to the disaster zone this weekend to escalate federal assistance.

With some estimates putting the number of homes and buildings destroyed at close to 10,000, state and federal authorities in the US South were still coming to terms with the scale of this week's devastation from the country's worst natural catastrophe since Hurricane Katrina in 2005.

Thousands of stunned survivors, many of whom had seen relatives and friends killed by twisters that obliterated whole communities, were camped out in the shattered shells of their homes or moved into shelters or with friends.

One disaster risk modeler, EQECAT, is forecasting insured property losses of between $2 billion and $5 billion from the havoc inflicted by the swarm of tornadoes that gouged through seven southern states this week.

"It is like living in some other world. Devastation is everywhere," said Pastor John Gates of the United Methodist Church in Pleasant Grove, Alabama, a community with a population of some 10,000 west of Birmingham.            

Alabama, the hardest-hit state, revised down its fatalities to 249 on Saturday after initially reporting 255 dead. At least 101 more deaths were reported in Mississippi, Tennessee, Arkansas, Georgia, Virginia and Louisiana.

Several thousand people were injured and hurt.

Stories of survival from the deadly twisters were still emerging but one report from a Jefferson County, Alabama emergency official of three people pulled alive from their wrecked home after three days turned out to be false.

The death toll, which is expected to rise, was the second highest inflicted by tornadoes in US history. In 1925, 747 people were killed after twisters hit the US Midwestern states of Missouri, Illinois and Indiana.

Unlocking federal assistance, Obama late on Friday signed major disaster declarations for Mississippi and Georgia, adding to the one already signed for Alabama.

Secretary of Homeland Security Janet Napolitano, Federal Emergency Management Agency Administrator Craig Fugate, Housing and Urban Development Secretary Shaun Donovan, Agriculture Secretary Tom Vilsack and Small Business Administration Administrator Karen Mills were all due to visit devastated areas in Alabama and Mississippi on Sunday, FEMA said.