Five tornadoes touched down on Wednesday in the Denver area accompanied by icy hail, forcing the city's airport to divert dozens of flights although no damage was immediately reported, officials said.
Denver-area residents rushed for cover as three twisters hit the eastern suburb of Aurora within a half-hour period, while two more touched down in nearby areas, said meteorologist Jim Kalina of the National Weather Service's Boulder office.
A tornado watch for Denver was scheduled to remain in effect until 8 p.m. local time , the Weather Service said. But Kalina was not expecting any more tornadoes.
"Denver's kind of in the clear right now unless something else develops," he said.
Denver is not considered to be part of the so-called tornado alley, the region stretching from Texas to South Dakota that accounts for roughly a fourth of all U.S. tornadoes, but the metropolitan area gets several twisters a year.
The second half of May to early June, when winds often cross each other in the region, is the peak time for tornadoes in the Denver area, said Weather Service meteorologist Scott Entrekin.
Officials at Denver International Airport diverted 40 flights as a result of the tornado threat, said airport spokesman Heath Montgomery.
The airport's Twitter page showed a photo of dozens of construction workers taking shelter in a garage at the facility, and Montgomery said airlines were assessing potential storm damage to their planes.