Multiple people have fallen ill after opening a “suspicious package” delivered to the base of operations for Air Force One.

A spokesperson for Joint Base Andrews (JBA) in Maryland, near the US capital, Washington DC, said the building the package was opened in was evacuated and those taken ill were found to be in a stable condition by medical staff.

The package contained an unidentified white powder, CNN reports, citing unnamed sources taking part in an investigation.

The air base houses the US presidential plane and its support craft, and is where the president usually departs on trips.

The JBA spokesperson said the building in which the package was opened and a connecting building were evacuated “as a precaution” and a cordon established around the area.

They added: “First responders were dispatched to the scene, determined there were no immediate threats, and normal operations have resumed. An investigation is currently ongoing.”

Initial tests by a Hazmat team did not detect anything hazardous, according to CNN.

It reports that investigators are also assessing political propaganda that was included in the package.

It is unclear the extent or the nature of the illness suffered by those near the package when it was opened.