WASHINGTON (AFP) - Flights at the airport in Virginia's state capital Richmond were suspended on Tuesday and the terminal evacuated after a "serious" threat was phoned in, officials said.

On its Twitter feed (@Flack4RIC), Richmond International Airport said it had "received a threat by phone, deemed serious enough to evacuate the terminal as a precautionary measure."

Sniffer dogs swept the terminal, baggage areas and parking zones, while travellers were advised to check with their airlines for rebooking options, before the all-clear was given.

"Update: #RIC terminal, including airline desks and security screening, re-opened to the public," tweeted the airport four hours after the undisclosed threat was received.

More than a half-dozen airlines serve Richmond International Airport.