(CNN) -- A line of fast-moving storms and possible tornadoes stretching from the Gulf Coast states to Illinois left at least six people dead Friday and caused widespread damage to homes and businesses, as forecasters warned of more potentially severe weather.
Three people died in the small northwestern Arkansas town of Cincinnati, which reported power outages after the strong storm went through, said Ann Upton, Washington County's emergency management deputy.
Two additional fatalities occurred in Dent County, Missouri, according to Salem police spokeswoman Wanda Suhr.
While a sixth storm-related death happened at a home just north of Rolla, Missouri, about 106 miles southwest of St. Louis, said Phelps County Emergency Management spokeswoman Sandy North.
The storm injured residents and destroyed some 25 homes in Phelps County after it earlier left more than a dozen people hospitalized in northwestern Arkansas, medical officials said.
Missouri Gov. Jay Nixon declared a state of emergency.
"We have three confirmed deaths today. We have some other people with some significant injuries and that's why I declared a state of emergency. Our state emergency management folks are up and operating to assist the locals and provide whatever support is necessary," he told CNN.
The governor, who is expected to tour the affected areas Saturday, said officials are still working to access the damage.
In Arkansas, Washington Regional Medical Center spokeswoman Terry Fox said several people were also reported trapped under fallen debris in the storm's immediate aftermath in Benton County.
Six homes and four chicken production facilities were destroyed, while five homes suffered moderate to heavy damage, said Matt Garrity, Benton County's manager of emergency services.
A fire station, three buildings and one store were also damaged, said Garrity, and an airport that serves northwestern Arkansas was closed due to debris in the area.
"We are in part of tornado alley," he said. "So even a small storm does a lot of damage."
Emergency crews are currently surveying the extent of the damage and "making sure that no one is trapped," he said.
In Mississippi, a storm system knocked out power to nearly 20,000 homes in the central part of the state, said Mara Hartman, a spokeswoman for Entergy Corporation.
Elsewhere, the fast-moving storm caused injuries and damage in Pulaski and Laclede counties in Missouri, knocking out power at Fort Leonard Wood, a U.S. Army post that took a direct hit from a suspected tornado, accordingto Laclede County Emergency Management spokesman Gail Teter.
Four people at the base were treated for minor injuries after the storm hit, the army said. The tornado cut through several miles from the training areas into where families live.
The series of storms that moved through Oklahoma and into northwest Arkansas and southwest Missouri have reached speeds of 40 mph and passed through more populated areas in St. Louis, Missouri, and the surrounding municipalities.
Search and rescue workers were deployed to assess the storm's damage in St. Louis County, where there were reports of injuries, according to Mark Diedrich, the county's emergency management acting director.
CNN affiliate KMOV on Friday broadcast images of heavy damage -- including destroyed homes and overturned vehicles -- in Sunset Hills, Missouri, approximately 15 miles southwest of St. Louis.
"It's causing havoc," said Sunset Hills police spokeswoman Donna Palasky.
The storm also left heavy structural damage to buildings in its wake -- including a popular shopping center and Catholic church -- in the town of Fenton, some 18 miles southwest of St. Louis, said Fenton Deputy Fire Chief Jeff Heidbreder.
Emergency crews are surveying the damage, he said, but there were no reports of injuries.
In the nearby town of Ballwin, police spokeman Jim Heldmann said the storm caused heavy damage to homes and buildings, but no injuries were reported at this time.
The Arkansas Department of Emergency Management issued a tornado advisory as bad weather lingered in the state, instructing residents to seek shelter in their home's interior rooms or on its lowest floor.
"When a tornado is sighted, the most important rule is to get low and stay low," the statement said.
The threat of severe thunderstorms and possible tornadoes will continue through Friday evening across the Mississippi Valley and Tennessee Valley states, according to Greg Carbin, meteorologist for the National Weather Service.
CNN's Mark Bixler, Reynolds Wolf, Tom Laabs, Erica Henry, Aaron Cooper and Shelby Erdman contributed to this report.