by Juan Castro Olivera Juan Castro Olivera

TUSCALOOSA, Alabama (AFP) – Shocked Americans struggled Thursday to grasp the magnitude of the worst US tornadoes in decades, which carved a trail of destruction across the south, leaving 280 people dead and some communities virtually wiped off the map.

Disbelief and despair were written on the faces of residents of cities and towns in seven states crippled by the ferocious spring storms as they picked through the remains of destroyed homes, businesses and schools, in surreal scenes of devastation more common to war zones and massive earthquakes.

The severe weather killed at least 184 people and injured several hundred more on Wednesday in Alabama alone, authorities told AFP, and President Barack Obama said he would travel to the state Friday for a first-hand look at the devastation.

"The loss of life has been heartbreaking, especially in Alabama," Obama said Thursday at the White House, calling the destruction "nothing short of catastrophic" as he vowed to rush federal assistance to the Gulf Coast state battered by one of the deadliest tornado outbreaks in US history.

The storms "took mothers and fathers, sons and daughters, friends and neighbors -- even entire communities," he said.

States of emergency were declared from the central state of Oklahoma to Georgia on the eastern seaboard, and governors called out the National Guard -- including 2,000 troops in hardest hit Alabama -- to help with rescue and cleanup operations.

"We had a major catastrophic event here in Alabama with the outbreak of numerous long-track tornadoes," said Governor Robert Bentley, who declared a major disaster for the state and estimated that up to a million people were without power.

Emergency responders were combing communities in a sprawling rescue and recovery effort, and experts said it would take days to get a true picture of the devastation.

Thousands of residents will spend the night in shelters, officials said.

By all accounts the destruction was severe, and John De Block, a National Weather Service (NWS) meteorologist in Birmingham, Alabama, warned people to brace for nearly unprecedented damage.

"There were direct hits on two towns, Hackleburg and Dadeville," De Block told AFP, saying colleagues surveying the area reported that Hackleburg, population 1,500, was "90 percent destroyed."

Most of the homes there were built on slab foundations, and "the slabs have been swept clean in several locations," he said.

Across the region officials reported at least 284 deaths, but as the residents and emergency workers began to mop up and assess the damage the toll was likely to rise.

"In fact, we're sure it will," Bentley said, echoing concerns of officials across several states in what meteorologists described as the deadliest US tornadoes since 310 people were killed on April 3, 1974.

The NWS had preliminary reports of more than 300 tornadoes since storms began Friday, including more than 130 on Wednesday alone.

In the city of Tuscaloosa, Mayor Walter Maddox told CNN the tornado had "obliterated blocks and blocks" of his city, leaving 36 people dead there -- 21 more than officially reported by Alabama's government -- more than 600 wounded and several more missing.

"Infrastructure has been absolutely devastated," he said. "When you look at this path of destruction, likely five to seven miles (eight to 11 kilometers) long and half a mile to a mile wide, I don't know how anyone survived.

"There are parts of this city I don't recognize," he added.

It was also a dark day for Birmingham, Alabama's largest city with more than a million residents.

Mayor William Bell spoke of "whole neighborhoods of housing, just completely gone. Churches, gone. Businesses, gone."

The area, he told National Public Radio, "seems like a bomb has been dropped on it."

Incredulous Birmingham residents assessing the damage were counting their blessings at having survived, while others were distraught over the loss of their loved ones or homes.

"There were two-by-fours (wooden beams) falling out of the sky," convenience store manager Jack Welch said, adding "there were well over 30 homes destroyed" just behind his store.

State officials reported at least 33 dead in Tennessee, while in Mississippi storms killed 32 people.

Fourteen died in Georgia, 11 in Arkansas, eight in Virginia, and another two killed in severe flooding in Missouri, state officials said.

"Oh my God, our town is in pieces," said Tim Holt, a clerk at a local hotel in Ringgold, Georgia. "We saw the funnel cloud coming and I ran into the bathroom with my wife and daughter."

"It's an 80 percent loss in our town," he added.

The storms come after a wet spring and a winter of heavy snowfall which has left the ground saturated and rivers running high.

Several eastern states were on tornado and severe thunderstorm alert Thursday, while another major storm system is forecast to bring heavy rain and high winds on Saturday.