The tornado that killed two people in Quapaw, which is near Oklahoma's borders with Kansas and Missouri, struck the city at around 5:30 p.m., Ottawa County sheriff's dispatcher Colleen Thompson said.
Ottawa County Emergency Management director Joe Dan Morgan said Quapaw, which has about 900 residents, was heavily damaged by the tornado.
"Looks like about half of town got extensive damage as well as the fire department," Morgan said.
After hitting Quapaw, the twister continued northward into Kansas and struck Baxter Springs, about 5 miles away, said Morgan, whose staff was still assessing the extent of the damage in Quapaw.
Cherokee County, Kan., sheriff's dispatcher Josh Harvey said the tornado that hit Baxter Springs injured several people and caused extensive damage, but that no deaths had been reported. He said first responders were going from house to house checking on the wellbeing of the community's roughly 4,200 residents.
That twister was one of several that struck Sunday in a large swath of the Plains, Midwest and South affected by the storm system. Tornadoes also touched down in Arkansas, Nebraska, Iowa and Missouri. Tornado warnings, which indicate the greatest threat of a strike, were also in effect for parts of northeastern Texas and western Tennessee as of 7:30 p.m. CDT.
A large tornado formed about 10 miles west of Little Rock, Ark., Sunday night and stayed on the ground as it moved northeastward for at least 30 miles, carving a destructive path through several suburbs. Although there were no immediate reports of injuries, television footage showed badly damaged buildings and vehicles, and trees that had been stripped bare of their leaves and smaller branches.
Some of the worst damage appeared to be in the city of Mayflower, and authorities issued tornado emergencies for the nearby communities of Maumelle, Morgan, Saltillo and Vilonia.
One of Sunday's twisters touched down northwest of Joplin, Mo., where a massive tornado in May 2011 killed 161 people, injured many others and leveled a large swath of the city. Sunday's twister didn't hit Joplin.
Forecasters also asked people to be alert Sunday for possible tornadoes in a wide swath of the Midwest and south, stretching from Omaha, Neb., south to Texas and east to northern Louisiana and Mississippi.
"The greatest risk for a few intense tornadoes will exist across much of Arkansas perhaps into western and central Missouri," a weather service advisory said.
The first reported tornado from the storm system touched down Sunday afternoon in a rural area in central in Nebraska. The weather service said it remained on the ground for only a short time, and there were no immediate reports of damage.
Tornado watches - which means twisters could develop but aren't an immediate threat - were in effect for states as far west as New Mexico and as far east as Tennessee, and the system produced storms that were moving through the region in waves. Watches were also issued for Kansas, Missouri, Mississippi, Nebraska, Iowa, Arkansas, Oklahoma, Texas and Louisiana.
Areas that don't get tornadoes could still get buffeted by hail and powerful straight-line winds. Forecasters warned of hail stones as big as baseballs and wind gusts that could reach hurricane-force - 75 mph or higher.
Gusts of up to 60 mph were registered during a story that hit southeastern Iowa on Sunday that damaged several buildings, including a barn that injured someone when it was blown over.
Earlier Sunday afternoon, a strong line of storms moved through west-central Missouri, bringing winds that reached 70 mph hour near Chillicothe, Mo., that toppled some trees.
The Missouri Highway Patrol also reported a tractor-trailer was blown onto its side on Interstate 70 about 30 miles east of Kansas City about 1 p.m. No one was injured. The weather service received a report from Plattsburg, Mo., where an anemometer measured 58 mph before it blew away. Golf ball-sized hail was reported at Overland Park, Kan., and Trimble, Mo.
Severe thunderstorm watches covered portions of Iowa, Illinois and Missouri through Sunday night. The primary threats were damaging wind gusts and large hail.
To the southeast, northern Louisiana and Mississippi were bracing for severe storms along with the possibility of flash flooding. The predictions prompted Barksdale Air Force Base near Bossier City, La., to cancel its air show on Sunday. The National Weather Service said northern Alabama could see rain and flash flooding, while central and northern Georgia could see storms and heavy rain.
Sunday was the third anniversary of a 122-tornado day, which struck parts of Mississippi, Alabama, Tennessee, Virginia and Georgia and killed 316 people.
Meanwhile, runners in Oklahoma City took shelter early Sunday as hail and high winds delayed the Oklahoma City Memorial Marathon by 105 minutes to let a severe thunderstorm pass through.