An unidentified white powder was involved, according to media reports.

Several people have fallen ill at a key US airbase that hosts Air Force One after a package reportedly containing unidentified white powder was delivered to the facility.

The incident at Joint Base Andrews (JBA) in Maryland on Thursday prompted an evacuation of two connected buildings, according to officials.

A JBA spokesperson confirmed to the media that "multiple individuals felt ill" after a person opened a "suspicious package" that had been delivered to the base.

As a precaution, the building where the incident occurred was evacuated and cordoned off and the scene was examined by HAZMAT teams, which detected no immediate threat.

Officials have not disclosed the contents of the package. However, CNN has reported, citing two sources familiar with the investigation, that the delivery contained an unidentified white powder and was accompanied by political material.

An initial field test conducted by a HAZMAT team reportedly did not detect any hazardous substances, though the composition of the material has yet to be confirmed, CNN said.

Joint Base Andrews is the home base for Air Force One and other aircraft used by senior government officials. US President Donald Trump had been at the facility the previous day, although there is no indication of any connection to the incident.

The inquiry into the incident has been turned over to the Office of Special Investigations.

The US has previously faced scares involving suspicious powder in the mail. The most notable case occurred in 2001, when anthrax-laced letters were sent to media outlets and members of Congress, killing five people and infecting 17 others. The perpetrators have never been found.

Since then, authorities have remained on heightened alert to sporadic reports or threats of powder-filled envelopes sent to government offices, election facilities, and military installations, most of which have proven to be hoaxes or non-hazardous substances.