The series of tornadoes and thunderstorms that have swept past the southern U.S. state of Alabama and seven others, have claimed at least 311 lives so far and have left the city of Tuscaloosa in ruins, flattening entire city blocks.

In Alabama alone, the twisters claimed 204 lives so far, including 36 in Tuscaloosa.

Alabama Governor Robert Bentley said he has deployed 2,000 National Guard troops to assist in the search-and-rescue efforts. There is some massive devastation out there, he said.

Though the twisters have reportedly damaged the Browns Ferry nuclear power plant in northern Alabama, creating power cut in the entire state, Bentley said the plant's safety systems are working, dismissing fears of radiation leak.

Weather experts said the tornadoes and the thunderstorms are the worst to hit the United States in four decades. They said the tornadoes that hit Tuscaloosa could have been on the ground for 176 miles, with wind speed between 167 and 200 mph.

In Tennessee and Mississippi over 70 were reported killed.

Georgia, Arkansas, Missouri, Virginia and Kentucky were also badly affected.

The tornadoes were termed catastrophic by President Barack Obama. Obama said the federal government will do everything it can to help the region recover. In a matter of hours these deadly tornadoes...took mothers and fathers, sons and daughters, friends and neighbors, even entire communities, the president said.

See below a video of the destruction left behind by the 'perfect storm.'