Photo courtesy DCist reader Ethan L.

The 700 block of First Street NE is currently closed while crews respond to a suspicious substance found in a nearby building.

D.C. police responded to 750 First Street NE at about 1:40 p.m. for a suspicious package call. There they discovered an unknown white powdery substance, and subsequently requested D.C. Fire/EMS and Hazmat crews to assist at the scene, Fire department spokesperson Pete Piringer said. Those crews are currently staging their response in the vicinity, causing traffic delays and temporary road closures around Union Station. The building has also been evacuated as a precaution.

The address is a large office building that is home to numerous organizations, including, among many others, the National Association of Attorneys General and the National Association of Social Workers. There’s no word yet on where in the building the substance was discovered. There have been no reports of illness or injury as a result of the incident, according to Piringer.

UPDATE 4:15 p.m. The package was apparently sent to the American Psychological Association, and was received in the first floor mail room. Three people who were in the mail room decided to take themselves to the hospital to be evaluated, but they have no discernible symptoms. Several blocks of First Street NE are still blocked off. The substance has yet to be identified, according to Piringer.