South Carolina residents on Tuesday reeled under the effects of weekend flooding that killed at least 11 people and left tens of thousands without power or drinking water.

President Barack Obama signed a disaster declaration on Monday, making federal aid available to the southern state that has been drenched with a level of rain that -- as Governor Nikki Haley put it -- the region has not seen in 1,000 years.

A tropical air mass over much of South Carolina starting Thursday dumped 14 inches (36 centimeters) of rain, a new record, the National Weather Service said.

That downpour caused sudden and dramatic flooding, bursting dams and leaving residents scrambling for safety.

"It was traumatic, I've never seen anything like this," said Phyllis Jones, a 50-year resident of Columbia, the state capital.

Jones lives in an upstairs apartment at a complex called Willow Creek, whose namesake waterway inundated the ground-floor units on Sunday.

The rain tapered off Monday and water receded, but Jones said she has not left her apartment "for fear of looting."

She had stocked up on drinking water ahead of the flooding, but then she lost power.

At least four people have been killed in weather-related traffic accidents, while seven more have drowned, the Charleston Post and Courier newspaper reported.

Those killed included five trapped in vehicles overcome by flood water, the paper reported, citing state officials.

Government officials urged people to stay home, and warned that flooding was expected to continue for several days.

Some 26,000 people had no power and 40,000 had no drinking water, Haley told reporters on the outskirts of the capital Columbia, which has been especially hard hit.

"This is not over," she warned.

- Torrential rain -

Many shaken residents fled to shelters, while others were evacuated from their homes by boat and air. Hundreds of roads and bridges were closed to traffic due to heavy flooding

"Our house, car -- we lost everything. Everything is underwater. We didn't get time to do nothing," said Patricia Harde, 48, who fled with her two adult daughters and their four small children, including a four-month-old baby, to a school-turned-shelter.

"The water was coming up to my waist when we left," she added.

"I went back to try to get things for the baby -- milk and Pampers -- but I couldn't. Everything was covered in water."

Firefighters rescued them. But while some rode in a boat, others had to walk through the rapidly rising, dirty water.

"I'd always seen this on TV, but I never thought it would happen to us," said Harde, whose birthday was Monday.

In South Carolina there are some 2,400 dams, almost all privately owned, according to media reports. At least nine of them have failed in the past days, Columbia Mayor Steve Benjamin said.

- 'Everything is lost' -

"It's the first time I've ever seen this," said Ken Hart, 49, as he sat on a cot at a Red Cross shelter at St Andrews Middle School in Columbia.

Several people slept while children played on a stage in the school theater.

Rescue personnel and repair crews were hard at work, Haley said, adding that 25 helicopter evacuations have been conducted.

Across the state, some 550 roads and bridges -- some of which were completely washed out by flash floods -- were closed to traffic. Main roads, even major highways, seemed like rivers.

In the historic coastal city of Charleston, population 130,000, more than 900 people were housed in emergency centers Monday.

Eva Gadsen, 72, heard someone at her door Sunday morning telling her that she needed to get out.

When she opened the door, the water rushed in. "The water was at my waist," she recalled.

"When we got around the corner, I saw the fridge coming out of my apartment, going across the water," she said.

"Thank God I am still alive and I have a place to stay. People who went back to the building say everything is lost."

Schools were closed in Columbia, along with most government offices and shops.

Water distribution points opened in the city for 1.5 hours before the curfew, in place for a second night from 7:00 pm to 6:00 am.

Drinking from the city system was considered unsafe after breaches in the canal supplying the city.

Local media reported firefighters were pumping fresh water to the water systems of Columbia's hospitals, which, like the rest of the city, had been advised to boil water before using it.