PHOTOS: Deadly tornadoes kill over 300 in US

Over 300 people were killed when dozens of deadly tornadoes, triggered by the storms of near-epic proportions wiped out entire towns across six southern American states, officials said on Friday.

In Alabama alone the toll has reached 204, with more than 1,700 injured. President Barack Obama and the First Lady were to travel to the worst-hit state today for a first-hand look at a still unfolding human tragedy.

A breakdown provided by Alabama Governor Robert Bentley's office showed that violent weather claimed lives in 16 Alabama counties.

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Dave Imy, a meteorologist with the National Weather Service's Storm Prediction Centre said the number of deaths was the most in a tornado outbreak since 1974, when 315 people died.

Entire neighbourhoods were leveled and hundreds of thousands of people were without power, CNN reported. Bentley estimated as many as half a million to a million people were without power statewide.

Long before the death toll mushroomed, governors in Alabama, Mississippi and Georgia had declared states of emergency within their borders. Virginia also followed suit.

US President Barack Obama announced that he had approved Bentley's request for emergency federal assistance, including search and rescue support.

"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.

Said to be one of the deadliest tornado day in the US since 310 people lost their lives on April 3, 1974; the natural calamity has killed more than 150 people in the worst hit Alabama, besides those in the other States of Mississippi, Georgia, Arkansas and Tennessee.

"In a matter of hours, these deadly tornadoes ... took mothers and fathers, sons and daughters, friends and neighbors, even entire communities," Obama said.

"The scenes of destruction and devastation touch the hearts of every American, and demand clear, united, and compassionate action from our nation's leaders," said Democratic leader Nancy Pelosi.

Georgia Gov Nathan Deal toured the tornado area this morning and said, "It's hard to imagine nature can be this devastating."

The governor said it was a remarkably wide swath of twisters and noted there were multiple tornadoes in some areas.

Greg Carbin, warning coordination meteorologist at the National Weather Service, told ABC news that the area can expect mild weather for the next few days but he could not predict whether more killer tornadoes were on their way.

"May is usually the most active tornado month," Carbin said, adding "Will it maintain the activity of April? We just cannot say."

Tornado watches were issued into Thursday night along nearly the entire East Coast -- from Georgia to the Boston area -- a designation that carries the possibility of severe storms and winds in excess of 100 mph.

Eric Hamilton, 40, lived in a poor area of Tuscaloosa called Alberta City, which residents now describe as "gone." He wiped tears off his cheeks.

"I've never seen so many bodies," he told Seattle Times, adding, "Babies, women. So many bodies."

Meteorologists are on the ground examining the damage to try to get a precise handle on the number of distinct tornadoes and their intensity.

Damage was made worse by earlier storms, which left the ground so soaked that, instead of winds just snapping trees and branches, they uprooted entire trees and tossed them onto power lines, said Michael Sznajderman, a spokesman for Alabama Power Co.