Emergency officials counted casualties, picked through rubble and braced for more carnage Tuesday as a massive, slow-moving but extremely violent storm system refused to release its grip on a wide swath of the nation.
Tornado warnings were posted for parts of eastern North Carolina, and there were reports of funnel-shaped clouds.
Seventeen people were reported killed Monday after tornadoes roared through Alabama, Mississippi and Tennessee.
The preliminary death toll from vicious weather since Sunday rose to 35 with the death in Iowa of an 18th victim of Sunday's weather.
The prolonged weather pattern was unusual, forecasters said, noting that Monday and Tuesday marked the first time in 25 years with 10 or more tornado deaths for two straight days.
The twisters and high winds flattened homes and businesses, uprooted trees and flipped cars across sections of the South and Midwest. The National Weather Service was investigating reports of almost 100 tornadoes. And the destruction may not be over yet.
More than 60 million people from southeastern Michigan to the central Gulf Coast to the Carolinas and southern Virginia are at risk of severe storms and tornadoes Tuesday, AccuWeather meteorologist Alex Sosnowski said.
Mississippi and Alabama remained the states with the highest risk of severe weather, with cities such as Meridian, Miss., and Birmingham, Ala., in the cross hairs for tornadoes, the weather service reported.
The East Coast was not exempt. A forecast of ongoing heavy rain caused the weather service to issue flash flood watches from northern Florida to southern New England.
Mississippi was the hardest hit Monday. The tornado that hit the Louisville, Miss., area was given a preliminary rating of at least EF4 by the National Weather Service. EF4 tornadoes have winds of 166-200 mph, making the Louisville twister the most powerful one to hit the U.S. this year.
Twelve deaths were reported in the state, nine of them in and around Louisville, a town of about 6,600 people. State Sen. Giles Ward said he was huddled in a bathroom with his wife, four other family members and their dog Monday night as a tornado destroyed his two-story brick house and turned his son-in-law's SUV upside down onto the patio in Louisville.
"Our family is OK, thank goodness," Ward told The Clarion-Ledger in Jackson. "Our house as well as all the houses in our neighborhood it appears are destroyed. But our family is safe."
Later, he texted: "I have never prayed so hard in my life. God is good. All we have lost is stuff."
In Tupelo, Miss., dozens of buildings were damaged and 30 people sought treatment at Northeast Mississippi Medical Center. Four people were admitted.
Two deaths were reported in Tennessee. In Lincoln County, the National Weather Service lifted an initial tornado warning shortly after 7 p.m. Monday, but at 8:24 p.m. it warned a tornado was coming. "Catastrophic damage likely with storm in Lincoln County," the message read. "170 (knots) of rotation with debris extending above 20,000 feet."
Within minutes, the warnings grew more dire with winds exceeding 190 mph, The Tennessean reported. Two people were killed in Lincoln County and several homes were destroyed, The Tennessean reports.
The warning seemingly came out of nowhere, said Chris Murdock, who lives 4 miles from a damaged elementary school. Although he and his family didn't see the tornado, the gusts and hail they saw as they went to a friend's basement were enough for him to know this wasn't an average spring storm.
"Just by the looks of it, you could tell something terrible was happening," he said.
In Alabama, University of Alabama student John Servati, a member of the Crimson Tide swim team, was killed when he took shelter in the basement of a Tuscaloosa home and a retaining wall collapsed on him. In Athens, Ala., the Limestone County Sheriff's Department reported two deaths from a twister that hit a mobile home park west of the town.
In Arkansas, the death toll from Sunday's tornado stood at 15, 11 of them in Faulkner County, KTHV-TV reported. The tornado has been given a preliminary rating of at least EF3 (136-165 mph winds) by the National Weather Service, one of only two EF3 tornadoes to hit the USA so far this year.
It was the deadliest single tornado in Arkansas in 17 years, the weather service said.
President Obama has sent his condolences to those affected by tornadoes and promised that the federal government would help in the recovery.
"Your country will be there to help you recover and rebuild as long as it takes," Obama said.
Contributing: William M. Welch, William Cummings; The Associated Press