The annual Cambridge Dance Party drew a reported 30,000 people last year. (Photo: David Kong)

The free annual Cambridge Dance Party that started with only 500 attendees in 1996 will likely have more than 30,000 this year, when it takes its place in front of City Hall for four hours on the final Friday in June.

“Generally, the crowds have increased year over year for the dance party, so we are anticipating a potentially larger crowd this year,” said Jeremy Warnick, director of communications and media relations for Cambridge police.

DJs spin the music and a colorful light show begins as dark falls, “adding to the magic” of an evening held so the community can celebrate summer together, according to the City Manager’s Office. And residents in a city with a reputation for the cerebral don’t just show up, but actually dance.

“It’s the kind of event that reminds you that Cambridge isn’t just a city with a few big schools and lots of smart people,” writer Julia Swanson said after 2014’s party, “but a vibrant and fun community to be part of.”

The street is closed off in front of City Hall to allow for crowds, which grew to 5,000 by 2012, reportedly doubled the next year, hitting 12,000 by 2014 and leaping to a potential 30,000 last year when coinciding with an anniversary celebration for same-sex marriage in Cambridge.(Maryellen Carvello, with the City Manager’s Office, cuts those estimates by a full third, and the city lowballs its estimates when requesting entertainment permits from its own License Commission.)

The event has typically been safe despite the crowds, with plenty of police presence and few incidents or arrests over the years. With police expectations for sustained bigger crowds, security plans “continue to be defined and evaluated,” Warnick said. “We’re still in the planning process.”

The party runs from 7 to 11 p.m. June 30 at City Hall, 795 Massachusetts Ave., Central Square. Massachusetts Avenue is closed to traffic between Prospect and Bigelow streets during the party, and the No. 1 bus line ends in Central Square at 6 p.m., but is expected to resume full service by midnight.