Crowds had been gathering at the mall for Wednesday night's Fourth of July festivities -- a concert emceed by Tony Danza with performances by Little Richard, Bebe Neuwirth and the National Symphony Orchestra, capped off by a fireworks display over the Washington Monument at 9:10 p.m. EDT.
CNN said the concert had been postponed, but WCBS-TV later reported that authorities said the activities would continue as planned, and expected crowds would be allowed to return to the mall around 7:30 p.m.
At around 5 p.m., the Park Service closed off checkpoints visitors needed to pass through to gain access to the mall, and advised those who were already there to seek shelter.
CNN said a tornado warning had been posted for nearby Howard County in Maryland, and for Fairfax County, Va.
McPhee, Cokas 'working on their marriage' after affair
Ohio bar shooting arrested, charged with murder