Americans in the southern and eastern US braced for more violent weather Tuesday after a string of tornadoes and other storms killed at least 29 people, news reports said.

Some 75 million people were at risk from storms that could unleash hail, winds and twisters on the affected regions, according to the National Weather Service.

The toll from two days of violent weather reached at least 29 Monday in at least six states, CNN and other media reported.

After violent weather Sunday that killed 17, most of them in Arkansas, the new deaths included eight in Mississippi on Monday, CNN reported, quoting the state emergency management agency.

The governors of Alabama and Georgia declared state-wide emergencies.

In the Mississippi town of Louisville, the storm snapped trees in half and stripped them of their branches. Sheet metal twisted itself around road signs and tree trunks, CBS News reported.

Mississippi Senator Giles Ward hunkered down in a bathroom with his wife, four other family members and their dog Monday as a tornado destroyed his two-story brick house and flipped his son-in-law's SUV upside down.

"For about 30 seconds, it was unbelievable," Ward said. "It's about as awful as anything we've gone through," the network quoted Ward as saying.

In the hardest-hit parts of Arkansas, emergency crews intensified their search for survivors of Sunday's twisters.

Dozens of Arkansas National Guard troops were assisting local authorities with medical evacuations, fresh water deliveries and search and rescue operations.

In the town of Vilonia, police chief Brad McNew said the town of 4,000 had been rendered unrecognizable.

"It's houses completely down to the foundations," he told NBC television.

Rescuers used searchlights in blacked-out areas Sunday night, sifting through mountains of rubble in the hopes of finding someone alive.

The Arkansas Department of Emergency Management said 14 people had been killed in the state.

McNew said more would have been killed if not for emergency sirens that warned people the twister was about to hit.

"I went to a tornado shelter myself with my family which was a couple miles away from where we were at. A lot of people in the community were there. And so, it did work," he said.

"If you see the destruction that is here, even though we've lost some lives, there are many lives that was saved because of the storm warnings."

Vilonia was struck three years ago by a tornado that took almost the same path, but Sunday's twister was "a lot worse," McNew said.

Twisters also devastated large sections of the town of Mayflower, population 2,300, just northwest of the Arkansas state capital, Little Rock.

- 'Your country will be there' -

Speaking in the Philippine capital Manila at the close of a tour of Asia, US President Barack Obama offered condolences and promised federal government aid.

"I want everybody to know that your country will be there to help you recover and rebuild as long as it takes," he said.

The White House said Obama called Arkansas Governor Mike Beebe to offer federal assistance.

Sunday's tornado crushed large trucks like empty cans, homes were violently ripped in half, and entire residential blocks were reduced to rubble.

Some homes were uprooted from their foundations. In Iowa, the tornado also dumped heavy rain, snapped trees and lifted the roof off a medical center in the town of Oskaloosa.

Dozens of homes were also reported destroyed in nearby Kansas, although officials so far have reported no fatalities there.