Emergency officials were searching for survivors Monday in the aftermath of tornadoes that killed at least 17 people in the central and southern United States.

The ferocious storm system continued to threaten millions more on Monday, creating a tornado that tore through Tupelo, Mississippi, damaging hundreds of homes, downing power lines and toppling trees. Officials said there were no immediate reports of deaths or injuries.

On Sunday, the suburbs of Little Rock, Arkansas were the hardest-hit areas. Officials in the southern state say tornadoes killed at least 15 people there.

President Barack Obama expressed condolences to the victims Monday during a visit to the Philippines, and said the government will help the victims recover and rebuild.

The National Weather Service warned of potentially strong storms with tornadoes Monday in Louisiana, Alabama, Mississippi and Tennessee.

The storm system is hitting on the third anniversary of one of the worst tornado outbreaks in U.S. history, which killed more than 300 people and included nearly 300 reported tornadoes across the nation's southeast.