The number of fatalities increased after the Kansas Highway Patrol reported eight people died in a highway pileup caused by a dust storm in Sherman County on Friday. At least 50 vehicles were involved.
Missouri recorded more fatalities than any other state as it withstood scattered twisters Friday night that killed at least 12 people, authorities said.
The deaths included a man who was killed after a tornado ripped apart his home.
"It was unrecognisable as a home. Just a debris field," Coroner Jim Akers of Butler County said.
"The floor was upside down. We were walking on walls."
Dakota Henderson said he and others rescuing people trapped in their homes on Friday night found five dead bodies scattered in the debris outside what remained of his aunt's house in hard-hit Wayne County, Missouri.
"It was a very rough deal last night," he said, surrounded by uprooted trees and splintered homes.
Henderson said they rescued his aunt from a bedroom that was the only room left standing in her house, taking her out through a window. They also carried out a man who had a broken arm and leg.
Three deaths were reported in Texas, also in traffic collisions due to dust storms, and three more fatalities were confirmed in Mississippi, where tornado and severe weather warnings were issued, broadcasters including ABC and CNN reported.
The US weather agency NOAA issued further severe weather warnings. It cautioned that particularly strong tornadoes could occur in the state of Mississippi in the afternoon.
Officials in Arkansas said three people died in Independence County and 29 others were injured across eight counties as storms passed through the state.
"We have teams out surveying the damage from last night's tornadoes and have first responders on the ground to assist," Arkansas Governor Sarah Huckabee Sanders said on X.
She and Georgia Governor Brian Kemp declared states of emergency. Kemp said he was making the declaration in anticipation of severe weather moving in later Saturday.
The deaths came as a massive storm system moving across the country unleashed winds that triggered deadly dust storms and fanned more than 100 wildfires.
Extreme weather conditions are forecast to affect an area home to more than 100 million people.
Winds gusting up to 130km/h were predicted from the Canadian border to Texas, threatening blizzard conditions in colder northern areas and wildfire risk in warmer, drier places to the south.
The National Weather Service issued blizzard warnings for parts of far western Minnesota and far eastern South Dakota starting early on Saturday.
Snow accumulations of eight to 15cm were expected, with up to 30cm possible.
Winds gusting to 97km/h were expected to cause whiteout conditions.
Evacuations were ordered in some Oklahoma communities as more than 130 fires were reported across the state.
Nearly 300 homes were damaged or destroyed. Governor Kevin Stitt said some 700sq/km had burned in his state.
The State Patrol said winds were so strong that they toppled several tractor-trailers.
The Storm Prediction Center said fast-moving storms could spawn twisters and hail as large as baseballs on Saturday, but the greatest threat would come from winds near or exceeding hurricane force, with gusts of 160km/h possible.
Significant tornadoes continued to hit on Saturday. The regions at highest risk stretch from eastern Louisiana and Mississippi through Alabama, western Georgia and the Florida panhandle, the centre said.
Wildfires elsewhere in the Southern Plains threatened to spread rapidly amid warm, dry weather and strong winds in Texas, Kansas, Missouri and New Mexico.
High winds also knocked out power to more than 200,000 homes and businesses in Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana and Michigan, according the website poweroutage.us.
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