More than 1 million customers are without electricity in Southern states on Thursday in the wake of devastating storms with tornadoes which have officially killed 305 people, mostly in Alabama.

Of the 305 dead, 204 were from Alabama, a spokeswoman for the state's emergency management agency told Agence France Presse.

People's lives have just been turned upside down, Gov. Robert Bentley told reporters on Thursday. It affects me emotionally. When I fly over this, it is difficult.

I have to separate myself emotionally from this because I'm the governor of the whole state, but this is my home. I love the people of Tuscaloosa, Bentley said. We're going to get through this because the people of Alabama are resilient and they care about each other.

This may be the worst natural disaster in Alabama's history, Bentley said.

Tuscaloosa Mayor Walter Maddox told reporters the damage is beyond a nightmare.

There are parts of this city I don't recognize, and that's someone that's lived here his entire life, he said.

Alabama Power estimated that 297,000 customers had no electricity on Thursday evening, while the Tennessee Valley authority said 641,000 people had no power. Nearly another 50,000 in Georgia didn't have power either.

The top federal disaster official met with Bentley to help coordinate response on Thursday ahead of a visit tomorrow by President Barack Obama.

Throughout this storm, the heroes have been the first responders, neighbors, volunteers and many others who have been working day and night to protect the public's health and safety, said Craig Fugate, director of the Federal Emergency Management Agency.

At FEMA, we're just one part of this team, and we're continuing to work closely with our state and local partners and tribal governments to make sure they have all the support they need for the duration of this storm, he said.