The St Louis airport was closed on Saturday after a vicious storm that spawned an apparent tornado ripped through the area, damaging airport buildings and flattening some homes.

Glass and other flying debris at Lambert Airport sent travelers running for cover but caused few injuries, most relatively minor.

"We know the airport is closed," said National Weather Service meteorologist Ben Miller. "We're assuming that (a tornado) is what it was."

Incoming flights were being diverted to Kansas City with the St. Louis airport closed indefinitely, according to its website.

Television reports showed workers and cranes on Saturday morning cleaning debris from the roof of one terminal building where the storm had left gaping holes.

In some St. Louis area neighborhoods, large areas had been flattened, with homes destroyed and cars overturned or tossed onto lawns by the force of the storm.

"St. Louis City, St. Louis County and surrounding municipalities are actively assisting ... with cleanup efforts and safety review of all operations," the airport statement said.

The storm hit the area just before 6 p.m. Friday, according to emergency management officials. Two state highways also were closed because of debris and an estimated 20 homes were damaged in St. Charles County just west of the airport.

Power lines were reported down across St. Louis County and strewn vehicles blocking roads made it difficult for emergency personnel to get through. Thousands were without power on Friday night, according to utility Ameren Missouri.

The utility's outage map reported total outages numbering more than 42,000 early on Saturday morning.

The National Weather Service had flood warnings in effect for much of Missouri on Saturday, including flash flood warnings in some areas.

When the storm hit, sirens went off in the airport and police and other airport workers scrambled to rush hundreds of travelers into bathrooms and other interior areas to ride it out.

About half the windows at the airfield's main terminal were blown out as the storm passed, an airport official said.

Airport spokesman Jeff Lea said the worst was over in what seemed like 15 seconds. Five people were injured, with four of them taken to an area hospital but the injuries amounted to mainly minor cuts and bruises, Lea said.

The storm did extensive damage to the main terminal at the airport, ripping the roof off one concourse and blowing in the glass in gate areas as well as outlying areas in front of the terminal, including a parking garage, Lea said.

Mayor Francis Slay said the airport suffered significant damage and that the city and county have called "all hands on deck" to deal with damage at the airport.

Severe storms and tornadoes last week killed at least 47 people in several states. – Reuters