PASSENGERS are being allowed back inside San Antonio International Airport terminals after being herded onto the tarmac when a bomb threat was called into the US airport.

The call alleged three packages had been left inside a parking garage.

Airport spokeswoman Nora Castro said flights also were being allowed to land again at the airport on Wednesday.

But San Antonio Fire Department spokeswoman Deborah Foster said roads leading to and from the airport remain closed while bomb-sniffing dogs continue to search the parking garage.

Castro said the dogs at one point appeared to detect something suspicious in the garage but it turned out to be a false hit.

Foster said they didn’t find any device.

Foster said about 2000 passengers were cleared from two terminals after the evacuation order was called at 2.35pm local time on Wednesday (0535 AEST Thursday).