All flights in and out of a Washington DC airport were halted on Tuesday due to a bomb threat on a plane, with delays rippling across the US.

A security emergency was issued at Ronald Reagan Washington National Airport (DCA) at 11.30am ET. 

The ground stop was lifted after 1pm ET and replaced with a ground delay, causing average waits of 51 minutes and delays of up to 151 minutes for some flights.

DCA is scheduled to be under a security-related arrival management program until 11.59pm.

The bomb threat was made known after travelers stranded on the runway heard there was an incident on a United flight that landed from Houston, which was quickly surrounded by emergency vehicles.

Ben Radnor posted online: 'On a Delta flight waiting to take off to JFK. Apparently a bomb threat on a United flight that landed from Houston not long ago. Nothing is allowed to move.' 

The delays at DCA are now impacting the rest of the country, as grounded and late-arriving flights are creating congestion at other airports.

Passengers can expect knock-on delays nationwide, including at connecting hubs and in parts of Canada. 

A DCA spokesman told the Daily Mail that while flights were being held, crews were working to offload passengers on the United Airlines flight, which had been relocated to the east side of the airfield for precautionary measures.

'Metropolitan Washington Airports Authority police are conducting a thorough investigation with the assistance of multiple law enforcement partners,' the DCA spokesperson added.

'Several flights were diverted to other airports during the runway closure. 

'People meeting passengers or flying this afternoon should expect delays and check with their airline for updated flight information.' 

The threat is reported to have been referred to in leaked radio audio between the air traffic controller and the United pilot.

The recording, reported by NBC affiliate WRC-TV, said: 'I'm sorry I have to do this to you... We have an unconfirmed bomb report for your flight.

'We are going to get you away from the airport.'

S C Byrd, who was stranded at DCA, reported online that his flight was cleared for takeoff at 1.04pm ET. 

However, under the security-related arrival management program, only 30 flights per hour are allowed to land at DCA.

The incident happened just minutes before Transportation Secretary Sean Duffy issued a stark warning about the impact of the government shutdown on the airline industry. 

'If you bring us to a week from today, Democrats, you will see mass chaos, you will see mass flight delays,' Duffy said. 

'You'll see mass cancellations, and you may see us close certain parts of the airspace, because we just cannot manage it.'