It's an unseasonably warm October morning, barely past 9 a.m. in New York City, and already there is a line stretching five blocks from the heart of the Jacob K. Javits Convention Center on 11th Avenue.

Captain America, the Joker, Wonder Woman, the Predator and Thor all stood in line, jockeying to be first to buy collectibles, get autographs and a chance to see their favorite actors on stage.

For the 13th year, the Javits Center has played host to New York Comic Con (NYCC), an annual event launched by ReedPop, an offshoot of event organizer Reed Exhibitions.

At least 250,000 people bought tickets to attend the four-day conference that closed Sunday, quite a bit more than the 12,000 attendees from the convention's first year, Mike Armstrong, event director at ReedPop, told CNBC.

"It's definitely our biggest year yet," Armstrong said. "We've grown steadily every year since 2006. We sell out of tickets very quickly, we sell out of booth space very quickly, we don't really have any more room for sponsorship so, we know that we have to continue growing outside of the Javits Center."

ReedPop has expanded the convention beyond the 840,000-square-foot exhibition space at the Javits Center to six other locations nearby, including Madison Square Garden and the Hammerstein Ballroom. The conference hosted more than 420 panel discussions on topics ranging from Superman's 80th anniversary to female writers of "Star Wars" novels and comics.

The convention is estimated to have brought in more than $100 million for New York, as attendees pay for hotel rooms, take public transportation and dine at restaurants, according to ReedPop. Armstrong declined to disclose the revenue expectations for this year's show, but he did say that most of the conference sold out, including some of its off-site events. Passes cost roughly $50 a day to attend the conference.

Comic conventions have exploded into the mainstream in the last few years, bolstering attendance rates not only in New York, but in San Diego, Chicago, Atlanta and Seattle.

San Diego is arguably the most well-known comic convention of the year, hosting hundreds of celebrities for panels, signings and meet-and-greets as well as being the go-to place for studios to release major news about movies, television shows and comics. But New York Comic Con is actually the biggest by attendance.

San Diego's infamous convention draws more than 130,000 people each year and is estimated to generate an economic impact of more than $140 million on the city. The only reason that number hasn't grown is because the convention organizers cannot fit any more attendees into the exhibition center.