Police evacuated one of nine passenger concourses at Miami International Airport today when passengers began coughing and sneezing because of an airborne "irritant," officials said.
Airport officials ultimately determined that the irritant was likely to have come from a nearby airport expansion construction site and may have moved through air conditioning ducts.
Miami International is one of the busiest US airports and serves as a gateway to Latin America and the Caribbean.
The incident caused alarm in south Florida, where the first cases of anthrax contamination were reported last autumn after the September 11th attacks on New York and Washington.
Police and fire officials said the first emergency calls indicated several passengers were having trouble breathing at a security checkpoint.
Miami airport is one of the key hubs for the biggest US airline, American Airlines, a unit of AMR Corp, and the disruption at the airport was likely to cause delays.
"We do expect some delays - I don't know how many," American Airlines spokeswoman Ms Martha Pantin said.
Virgin Atlantic Airways, which has counter space in concourse A, next to the affected concourse, said its one daily flight would not be delayed and its employees had not been affected by the incident.