President Obama and the first lady traveled to the South this morning to view the destruction from violent storms that have left more than 300 people dead across seven states this week.
Obama's plane landed late this morning in the hardest-hit state, Alabama, where at least 210 people were killed.
A total of 312 people have been reported killed by the storms. Mississippi reported 33 fatalities, Tennessee had 34, Georgia with at least 15, Virginia had five, Arkansas with 13 and Kentucky had one drowning victim, authorities said.
"In a matter of hours, these deadly tornadoes ... took mothers and fathers, sons and daughters, friends and neighbors, even entire communities," Obama said Thursday.
Obama is expected to tour the wreckage while on his way to Cape Canaveral for the launch of the space shuttle Endeavour in Florida.
He pledged full federal government support for all those affected by the storms and signed a disaster declaration for Alabama to assist in recovery and clean-up efforts from the tornado destruction.
"We can't control when or where a terrible storm may strike, but we can control how we respond to it," Obama said during a news conference Thursday at the White House.
About 2,000 national guard members have been deployed to help in search-and-rescue efforts.
NOAA, the National Oceanic and Atmospheric Administration, estimated there were 173 tornadoes Wednesday, setting a new record for one storm system.
"These were the most intense super-cell thunderstorms that I think anybody who was out there forecasting has ever seen," meteorologist Greg Carbin of the National Weather Service's Storm Prediction Center told the Associated Press.
The twisters leveled cities such as Tuscaloosa, Ala., forced some nuclear plants to go offline, left thousands homeless and more than 1 million people without power.
It was the worst tornado outbreak since 1974, when storms killed 315 people, according to NOAA.
At least 32 people died in Tuscaloosa where early estimates indicated that the tornado that hit the city could have been on the ground for 176 miles, with winds between 167 and 200 mph.
John Brown is a storm chaser who videotaped the tornado that tore through Tuscaloosa with 200 mph winds.
He said it was by the far the worst tornado he has ever witnessed.
"I've never seen anything like it. When we saw it, It was really tear-jerky to see it destroy people's lives and property," Brown said.
It not only hit homes and commercial areas but destroyed much of the city's public works infrastructure.
Big Lots employee Matt Wilson said Wednesday's experience was horrifying.
"We were actually standing out in front of the store, watching it come towards us. It was hard to tell which direction it was coming in," Wilson said. "It was coming towards us, so we ran to the back and got under a metal structure back in the back. And that's honestly what saved us."
Tuscaloosa Mayor Walter Maddox asked people Thursday to stay off the streets and conserve water, and for gawkers to stay away. He said "sightseers" are only getting in the way of emergency crews.
"This is going to be a very, very long process" of cleaning up and rebuilding, he said. "During this time we ask for patience and we ask for prayers."
Also hit hard by the twisters was the town of Smithfield, Miss. At least 32 fatalities were reported killed statewide.
"I think the only word that accurately describes anywhere near what's happened, here, is devastation," U.S. Rep. Alan Nunnelee, R-Miss., said.
Nunnelee said federal help is also on the way for survivors and victims.
"We want to make sure that we get every bit of assistance that is available anywhere in the nation; make sure that it's available to north Mississippi.
ABC News Radio, Michael S. James, Mike Marusarz, Jessica Hopper and the Associated Press contributed to this report.