MAYFLOWER, Arkansas (CNN) -- Parts of the South and Midwest could be in for more severe weather Monday, a day after suspected tornadoes killed at least 18 people in three states, including 10 who died in one devastated Arkansas county.
"It's chaos here," said James Firestone, mayor of Vilonia, Arkansas, one of the two hard-hit towns in Faulkner County. "Our downtown area seems like it's completely leveled."
"There's a few buildings partially standing, but the amount of damage is tremendous," he said Sunday. "There's gas lines spewing. Of course, power lines down. Houses are just a pile of brick."
Widespread damage was also reported in the nearby Arkansas town of Mayflower.
"There were cars flipped everywhere, there were people screaming," James Bryant, a Mississippi State University meteorology student who witnessed the storm, told CNN's "New Day" on Monday. "It was a tough scene."
As rescue crews continued to search for anyone who may remain trapped and residents began the long job of cleaning up, forecasters warned of more potentially dangerous weather Monday.
About 3 million people were under a moderate threat of severe weather Monday, CNN meteorologist Indra Petersons said. About 24 million were at slight risk of severe storms, she said.
Monday's forecast calls for a moderate risk of severe thunderstorms, tornadoes and hail in parts of the South. Portions of Mississippi, Alabama, Tennessee and Louisiana are at the greatest risk, according to the Storm Prediction Center.
The storms also will stretch into the Midwest and Ohio River Valley, with much of Illinois, Indiana and Kentucky at a slight risk of severe weather, according to forecasters.
'A huge black cloud'
In Sunday's storms, at least 16 people died across Arkansas. In addition to the Faulkner County deaths, the Arkansas Department of Emergency Management said five people died in Pulaski County and one died in White County. Authorities reported one storm-related death in Oklahoma and another in Iowa.
The storms boiled up after nearly a week of forecasts calling for severe weather, including a rare "high risk" warning from the National Weather Service's Storm Prediction Center.
Resident Bryant Pruitt said he ducked into his house when he saw a storm cloud approaching from the southwest.
"It was huge. It was by far the biggest one I've ever seen," he told CNN affiliate KTHV. "It was a huge black cloud ... and I ran inside."
It was much the same in Mayflower, a town of 1,600 about 20 miles to the southwest.
Authorities shut down a section of Interstate 40 after a tornado "as much as a half-mile wide" roared through the area, according to the National Weather Service.
The heavily used road was littered with crushed and overturned trucks and cars.
CNN meteorologist Chad Myers, who was in Mayflower, estimated the winds from the storm were at 130 to 150 mph.
Emergency workers tended to the scene throughout the night. Shelters were set up at the high school and at a local church.
The city's official website said schools would be closed Monday.
In Vilonia, a community of about 3,800 people, the nightmare of a tornado strike is all too familiar. Another storm ransacked the town almost three years ago to the day and followed essentially the same path, the mayor said.
National Weather Service meteorologist Jeff Hood said that at least one long-track tornado began in Pulaski County northwest of Little Rock and moved northeast from there. The office will survey the damage in the coming days to determine the rating of the tornado and if any other tornadoes hit in the region, he said.
President Barack Obama offered his condolences to storm victims while on a four-nation tour of Asia.
"I want all affected to know FEMA is on the ground and will help Americans in need, and your country will be there to help and rebuild as long as it takes," he said from the Philippines.
'Tell the public to stay away'
Before the bad weather slammed into Arkansas, witnesses spotted a twister in the northeast Oklahoma town of Quapaw, where one person died, the Ottawa County Sheriff's Office said.
Joe Dan Morgan, the county's emergency manager, said rescuers were working in an area where a concrete wall crashed onto a car.
There were other reports of damage in the community, stretching thin local resources.
"Search and rescue is under way involving several agencies," county emergency dispatcher Kelly Flecks said. "Please tell the public to stay away so they can do their jobs. We can't confirm anything else at the moment."
Quapaw is near the border with Kansas and Missouri.
The same line of storms hit Baxter Springs, Kansas, just a few miles to the north.
Sixty to 70 homes and at least 20 businesses were reported destroyed, said Cherokee County emergency manager Jason Allison.
A tornado estimated to be three blocks wide rumbled through the town of 4,200, he said.
A sprawling storm front also hit eastern Iowa, killing a woman in the tiny community of Kinross in Keokuk County, the sheriff's department said.
The one bright spot amid Sunday's devastation were the forecasts that predicted the severe weather days ago, said storm chaser Brett Adair.
The advance notice helped save lives, said Adair, whose team witnessed the Faulkner County storm, then helped victims.
"This definitely was not something to take lightly," he said.
CNN's Devon Sayers and Chad Myers reported from Mayflower. CNN's Ed Payne reported and wrote from Atlanta. CNN's Dave Alsup, Matthew Stucker, Catherine E. Shoichet and Sean Morris contributed to this report.
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