Roofs were blown off, trees smashed into houses, cars flipped over, semitrailers blown off interstate highways and windows shattered.
There were no reports of injuries in the residential areas, despite the wide destruction in a heavily populated area about three-quarters of a mile west of the airport.
"We're assuming that (a tornado) is what it was," said National Weather Service meteorologist Ben Miller.
Flights from Lambert Airport, located within the city limits and about 5 miles northwest of the downtown area, were being diverted to Kansas City. The airport remained closed indefinitely on Saturday morning, with Monday expected to be the earliest it might open.
St. Louis Mayor Francis Slay said he was bringing in all personnel to get the airport reopened. Rich Bradley, the city's chief engineer, said crews would work 24 hours a day.
Nearby roads were clogged and damage was extensive at the facility.
In a nearby neighborhood of large homes with big yards and swimming pools, television reports showed a man wandering in the rubble holding up pictures and pieces of broken furniture in a house nearly destroyed by the winds.
It appeared dozens of homes, built within the last 15 to 20 years, had been destroyed.
No one was hurt but one woman who did not identify herself said, "I heard the train sound they all talk about and the air pressure dropped. Then it hit."
Power lines were reported down across St Louis County with vehicles overturned on area roads, making it harder for emergency personnel to get through and leaving thousands without power Friday night, according to utility Ameren Missouri.
It reported power still out to 37,000 people on Saturday.
The National Weather Service showed flood warnings in effect for much of Missouri on Saturday, including flash flood warnings in some areas.