One of the many spectators who attended FanExpo at the Metro Toronto Convention Centre on Saturday. (CBC)

Hundreds of people in Toronto found themselves waiting in long lines outside a massive comic book and science fiction convention on Saturday because of fears of overcrowding.

Even though they had already purchased tickets for FanExpo, many people were told they would have to wait outside because the crowd was at full capacity inside the north building of the Metro Toronto Convention Centre.

"I think they dropped the ball on how much size the convention centre uses this year," Scott Campbell told CBC News.

"We have to wait probably an hour or an hour and a half," said Campbell who waited on Front Street West dressed as a Cobra Commander, a character in the G.I. Joe franchise.

Urges expansion

Campbell suggested the organizers consider using both the north and south parts of the downtown convention centre next year to accommodate all the fans.

FanExpo is billed as the largest gathering of its kind in the country. It is aimed at people interested in gaming, horror, comic, science fiction and anime.

Those waiting outside in the sweltering late-summer heat could only gain access once other people inside decided to leave.

Featured guests are expected to include William Shatner and Michael Dorn, from the Star Trek franchise; Adam West, Burt Ward and Julie Newmar, from the Batman TV series; and Peter Facinelli from the Twilight movies.

The event runs until Sunday.