Bentley also reported the Browns Ferry nuclear power plant in northern Alabama automatically shut down after it lost power to its three units. The U.S. Nuclear Regulatory Commission said the plant's safety systems are operating as needed.

The Federal Emergency Management Agency has deployed teams to the region to assist in response efforts, after U.S. President Barack Obama declared a state of emergency in Alabama.

Bentley said Alabama was as prepared as it could be to face tornados, with winds averaging 400 to 500 kilometers per hour. That measure is the most destructive on the Fujita Tornado Damage Scale.

"When you have a catastrophic F 4 and F 5 tornado that hits, there is not much you can do to change the outcome of that," he said. "But we did have a good response from the weather bureau and we have had a good response from our Emergency Management Agency. We were prepared."

FEMA Director Craig Fugate said the violent streak of tornados that have struck the southern United States in recent weeks is not uncommon.

"Actually what we are seeing is springtime. Unfortunately many people think of Oklahoma as tornado ally and forget that the southeast United States actually has a history of actually longer and more powerful tornados that stay on the ground longer," said Fugate.

Severe weather that began Monday also caused dozens of fatalities in Georgia, Tennessee, Virginia and Arkansas, making it the deadliest series of storms to hit the southern U.S. region in four decades.