The fatal twister in Santa Rosa struck around 11 p.m. Saturday, said Brad Hyman, a dispatcher for the De Kalb County Sheriff's Department.
The victims' names were not released, but four children were among the injured. Three children were in critical condition and one was in serious condition Sunday, said Jennifer Benz, a spokeswoman for Children's Mercy Hospital in Kansas City.
The others' conditions were not immediately available.
The twister destroyed four mobile homes and knocked out power.
Mike Hudson, a meteorologist with the National Weather Service, said tornadoes were reported in six other Missouri counties, including one in Platte County that appeared a quarter-mile wide on video footage.
Capt. Frank Hunter of the Platte County Sheriff's Department said one home and eight outbuildings were seriously damaged and some buildings were destroyed. The tornado touched down around 6 p.m., but no one was injured.
Severe weather also swept through Nebraska, including at least two tornadoes in the southern part of the state. The storms injured two people and caused thousands of power outages. Much of the power was restored by Sunday.
The two people injured had been jogging in Omaha when lightning struck, authorities said. One man took a direct hit and the other was near the strike and knocked to the ground. Both were in serious condition, authorities said.