A section of the main terminal at Denver International Airport was evacuated because of a possible security threat, officials said.
An airport spokesman told AFP that police were evacuating the western side of the terminal but that flights were continuing.
"It's a possible physical threat," Heath Montgomery said, without elaborating.
"Vehicle traffic has been stopped on the west side of the terminal, however, passengers may continue to access the east side of the terminal."
Montgomery said that several airlines had ticket counters inside the area evacuated - including American Airlines, Aero Mexico, Lufthansa and British Airways - and flight delays were possible.
The security alert came in the wake of terror attacks in Brussels that left around 35 dead and scores more injured.
