All flights were grounded at a major airport in Washington DC, the Federal Aviation Administration said.

All departing flights at Ronald Reagan Washington National Airport were halted for over an hour from 11:18 am ET, with reports suggesting a "bomb threat". The main runway reopened at 12:50 p.m., and flights have since resumed, according to the airport.

Passengers were seen being removed from an aircraft on the runway. The FAA confirmed the plane is "away from the terminal" while investigations continue.

According to AirLive, the reported threat targeted the United Airlines flight UA512 arriving from Houston IAD. The aviation news outlet added that the Boeing 737 MAX 8 had been moved away from the terminal area while authorities conduct their investigation.

The Federal Aviation Administration, the US government agency responsible for the safety of civil aviation, has issued a statement.

.@FAANews statement on DCA security incident pic.twitter.com/YDe7ym3hfq

A video of the scene appears to show a crowd of police gathered on the runway behind a United Airlines plane, CBS affiliate WUSA reports.

According to Pete Muntean, a CNN correspondent covering aviation, the flights were halted due to "a bomb threat on a plane".

According to flight tracking site FlightRadar24, flights were paused due to an unconfirmed threat against a United Airlines plane. The aircraft was moved away from other aircraft at the airport.

All flights at Ronald Reagan Washington National Airport have been paused from 11:18 am ET.