A reported bomb threat halted flights at Ronald Reagan Washington National Airport on Tuesday, delaying travelers and forcing passengers on a flight from Houston to deplane on the runway, officials said.

The ground stop was issued by the Federal Aviation Administration after a United Airlines flight from Houston was directed to land on an adjacent runway away from the terminal around 11:30 a.m., where passengers were taken off the plane and bused to the terminal, according to airport officials.

Transportation Secretary Sean Duffy said a bomb threat triggered the response.

The 89 passengers and six crew members aboard the flight were coming from the George Bush Intercontinental Airport in Houston, a United Airlines spokesperson said in an email.

Travelers should expect delays throughout Tuesday, Crystal Nosal, a spokesperson for the Metropolitan Washington Airports Authority, said in an email. The Bureau of Alcohol, Tobacco, Firearms and Explosives was on the scene assisting the Arlington County Fire Department and the Metropolitan Washington Transit Authority with the investigation.

Jonathan Dean, a spokesperson for Baltimore Washington International Thurgood Marshall Airport, said some flights that were meant to fly from Reagan National are now leaving from BWI, but he could not confirm how many.

The stoppage came amid what is vying to be the longest government shutdown in history that has left airports in shambles as air traffic controllers call off due to not being compensated.

Earlier this year, a midair collision between a Black Hawk helicopter with two soldiers and an American Airlines jet carrying 67 people heading towards Reagan National, killed all involved. Many people aboard the American Airlines flight were Marylanders.

This story has been updated.