JOPLIN, Mo. -- Crews busted holes in concrete slabs and sifted through strewn home goods Tuesday as rescuers focused on crumpled big-box stores and apartment complexes in Joplin in a frantic search for survivors of the deadliest single U.S. tornado in about 60 years.
One team poked through the remains of a Home Depot store, while others searched a Walmart and wrecked apartments as the clock ticked down on another round of severe storms. A hunt through the rubble using search-and-rescue dogs was planned, and officials expected to test the city's nine warning sirens while the sun was still shining.
The Storm Prediction Center in Norman, Okla., warned of a moderate risk of severe weather later Tuesday in central and southeast Kansas and southwestern Missouri, which could include Joplin. The center raised the warning for severe weather in central Oklahoma, southern Kansas and north Texas to high risk, indicating that tornadoes will hit in those areas.
The Storm Prediction Center also issued a high-risk warning before a tornado outbreak in the South in April that killed more than 300 people.
"This is a very serious situation brewing," center director Russell Schneider said.
The massive tornado that ripped through the heart of the blue-collar southwest Missouri city of 50,000 people on Sunday was the deadliest on record in nearly six decades.
Sam Murphey, a spokesman for Gov. Jay Nixon's office, said Tuesday that 117 bodies had been found but he didn't know when or where the latest one was discovered. Fire chief Mitch Randles said he knew of only 116 bodies found.
Nixon has said 17 survivors have been found, but Randles said he knew of only seven.
"We're getting sporadic calls of cries for help from rubble piles ... most of those are turning out to be false," Randles said.
Rescuers found one person alive at the Home Depot on Monday, but they also discovered seven bodies under a concrete slab, officials said. Search-and-rescue team leader Doug Westhoff said team members have searched as much of the store's interior as they can and are now focused on what is under collapsed concrete slabs that once helped hold up the store. After the holes are drilled, dogs will be brought in to try to detect any human scent.
Randles said teams were taking advantage of the best weather they'd had in two days to go through every damaged and destroyed building. After seven people were pulled from rubble Monday, he and others said they hoped to find more survivors.
"It's really incredible the fact that we're still finding people," Randles said.
Westhoff also expressed hope, but said the outlook at the Home Depot was bleak because of the size of the slabs and magnitude of the collapse.
Until this week, the deadliest single tornado on record with the National Weather Service in the past six decades was a twister that killed 116 people in Flint, Mich., in 1953.
More deaths have resulted from outbreaks of multiple tornadoes. On April 27, a pack of twisters roared across six Southern states, killing 314 people, more than two-thirds of them in Alabama. That was the single deadliest day for tornadoes since the National Weather Service began keeping such records in 1950.
The agency has done research that shows deadlier outbreaks before 1950. It says the single deadliest day that it is aware of was March 18, 1925, when tornadoes killed 747 people. The day also saw what weather officials believe was the single deadliest tornado when one twister ripped through Missouri, Illinois and Indiana, killing 695 people. The most deaths from the tri-state tornado, which started near Gang, Mo., and ended near Princeton, Ind., were in Murphysboro, Ill., where the tornado hit an elementary school in session.
Sunday's tornado slammed straight into St. John's Regional Medical Center, one of the hardest-hit areas in Joplin. The hospital confirmed that five of the dead were patients - all of them in critical condition before the tornado hit. A hospital visitor also was killed.
The tornado destroyed possibly "thousands" of homes, Randles told The Associated Press. It leveled hundreds of businesses, including massive ones such as the Home Depot and Walmart.
Speaking from London, President Barack Obama said he would travel to Missouri on Sunday to meet with people whose lives have been turned upside down by the twister. He vowed to make all federal resources available for efforts to recover and rebuild.
"The American people are by your side," Obama said. "We're going to stay there until every home is repaired, until every neighborhood is rebuilt, until every business is back on its feet."
Richard Serino, deputy director of the Federal Emergency Management Agency, said local officials did "an unbelievable job" with the immediate response and that his agency would be there "for the long haul" to help with the recovery.
FEMA director Craig Fugate flew over the area Tuesday morning with Nixon, Murphey said.