What appeared to be a flash mob gathered in Center City shortly before 9 p.m. Saturday night, though the event ended quickly.

A witness to the event described the gathering as between 100 and 200 people, who gathered quickly at the intersection of 15th and JFK Boulevard, coming from several directions at once. Some of those who gathered were dancing in the intersection, blocking traffic in the area, the witness said.

Police, in about a dozen cruisers – and accompanied by an ambulance – responded quickly, and the crowd dispersed rapidly. There was no apparent damage.