A tornado has killed two people in Quapaw, Okla., an official tells the Associated Press, as a powerful storm front is moving through parts of the Plains, Midwest and South. 

Read more below from the Associated Press:

A tornado killed two people in Quapaw, a small community in northeastern Oklahoma, near its borders with Kansas and Missouri, Ottawa County sheriff's dispatcher Colleen Thompson said. She said the twister hit the city at around 5:30 p.m. and that the extent of the damage was still unknown.

Keli Cain, a spokeswoman for Oklahoma Department of Emergency Management, said agency staff members were headed to the Quapaw area to assess the damage. She said a local official reported that Quapaw's fire station was heavily damaged.

"We're hearing that there's quite a bit of damage to the north side of town," Cain said.

Tornado warnings, which indicate the greatest threat of a strike, were in effect for parts of northwest Mississippi and western Missouri as of 6 p.m. CDT. In addition to the tornado strike in Oklahoma, twisters also had reportedly touched down Sunday in Nebraska, Iowa, Kansas and Missouri.

A funnel cloud 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 wasn't expected to hit Joplin, the weather service reported.

A tornado reportedly caused damage in or near Baxter Springs, Kan., which is in the state's southeast corner near its borders with Oklahoma to the south and Missouri to the east.

Central Arkansas, including the Little Rock area, was a high risk of severe storms later Sunday, reported the National Weather Service's Storm Prediction Center in Norman, Okla.

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.