At least 16 people were killed on Saturday in Missouri and Oklahoma after tornadoes swept through the area, authorities in the two states said.
A swarm of tornadoes that struck southwest Missouri killed 10 people, Missouri Emergency Management spokeswoman Susie Stonner said.
"Communication to the area, which is mostly rural, is really bad. There are a lot of power outages. There may be additional deaths," she said.
Six people were also killed in the small northeastern Oklahoma town of Picher, officials said.
"Basically a 24-block area is virtually destroyed," said Michelann Ooten, a spokeswoman for the Oklahoma Department of Emergency Management.
She added that Oklahoma Gov. Brad Henry had ordered National Guard troops to arrive in Picher by Sunday morning to help in rescue and recovery operations.
Local television footage from Picher showed widespread devastation. Homes were ripped from their foundations, trees were stripped of leaves and sheet metal was twisted like paper.
Ooten said search efforts for missing people in Picher were shutting down as it was unsafe for rescuers to move through the rubble at night even with mobile floodlights.
"You need day break," she said. "That'll be the real story."
Picher is at the center of a massive federal clean-up of pollution from lead and zinc mining. Residents were being assisted with relocation from the community after high levels of lead were found in groundwater.
Most of the victims in Missouri were in Newton County in the southwestern part of the state near the Oklahoma border, Stonner said.
Howard Birdsong, the mayor of Neosho, a town of 11,500 that is the Newton County seat, said at least two of the deaths came when a tornado overturned a vehicle.
It appeared the twister carved a 15-mile path just north of town after striking neighboring Oklahoma. In some areas, the destruction is a half-mile wide, he said.
"There's an awful lot of property damage," Birdsong said by telephone. "From what I've seen many homes have been destroyed, some businesses, and some cars have been overturned, uprooted trees and power outages ... There are several dozen injured."
Hail the size of golf balls fell across parts of the region, and high winds damaged power lines. Trees were uprooted, and trucks blown over, the National Weather Service said.
"There appears to have been one large storm. How many tornadoes, we're trying to sort out now," said NWS meteorologist Ryan Kardell.