The death toll from this week's devastating tornados has risen to at least 343, making it the second-deadliest tornado outbreak in American history.

President Barack and First Lady Michelle Obama Friday toured the devastation left by tornadoes that hit Alabama earlier this week and the President approved a Major Disaster Declaration for the stricken state.

"We just took a tour, and I've got to say I've never seen devastation like this," the President said. "It is heartbreaking. We were just talking to some residents here who were lucky enough to escape alive, but have lost everything. They mentioned that their neighbors had lost two of their grandchildren in the process."

"I just want to make a commitment to the communities here that we are going to do everything we can to help these communities rebuild ... We're going to make sure you're not forgotten." Obama said.

By early Saturday morning, emergency management officials tallied 254 deaths in Alabama, 34 in Tennessee, 33 in Mississippi, 15 in Georgia, 5 in Virginia and 1 in Arkansas, the CNN reported.

A loss of power was reported at the Browns Ferry Nuclear Power Plant. Power is currently being supplied by emergency backup generator.

This is the deadliest tornado outbreak since March 1932, when 332 people were killed. The death toll is also the second-largest in the country's history, only below that of a 1925 tornado outbreak which left 747 people dead, according to the National Weather Service.

In the hardest-hit Alamba, the confirmed fatalities have soared to 254, according to the state Emergency Management Agency. In addition, more than 1,700 people were injured while several others still missing.

Chinese President Hu Jintao extended condolences to his U.S. counterpart, Barack Obama, on Saturday over the devastating tornados that swept through southern United States this week.

Hu expressed his deep sympathy and condolences to Obama, and through him to the American people, over casualties and property losses. He mourned the dead.

The Chinese president said he believed that American people will overcome the difficulties and rebuild their homes.

Home to the University of Alabama, Tuscaloosa is now struggling to get power and water supply back to city neighborhoods. In Alabama, up to one million homes and businesses remained without power Friday.

Because of looting reports, Walter Maddox, mayor of Tuscaloosa, has issued a curfew order and it was still in effect Friday night from 8 p.m. to 6 a.m. Saturday morning.

Nearly 3,000 National Guardsmen have been mobilized to support the disaster relief efforts, the Pentagon said. They were delivering tarpaulins and clearing roads after hundreds of homes and businesses were damaged.