Two men, both in their 70s, were confirmed dead as a result of an earlier tornado that hit Shawnee, said Elliott, the spokeswoman for the state medical examiner's office.
As many as 28 tornadoes were reported in Oklahoma, Kansas, Illinois and Iowa, according to the National Weather Service, with Oklahoma and Kansas the hardest hit. Some of those reports might have been of the same tornado.
A combination of factors -- including strong winds and warm, moist air banging against dry air -- means severe weather could continue sweeping across a wide swath of the United States for days, Petersons said.
"Keep in mind we have all the ingredients out there that we need," she said.
Tornado watches were in effect for portions of southeastern Kansas, western and central Missouri, northwest Arkansas, central and eastern Oklahoma and northwestern Texas until 10 p.m. (11 p.m. ET).