One of the largest Fourth of July fireworks shows in the nation was ruined in San Diego Wednesday after a glitch caused all the pyrotechnics to ignite all at once.

About five minutes before the Port of San Diego’s Big Bay Boom was to begin at 9 p.m., spectators saw a brilliant display of fireworks that shot up in only 15 seconds – an incredible disappointment to hundreds of thousands of spectators who had waited for hours for the 18-minute show (see video below).

The Big Bay Boom is advertised as one of the largest fireworks shows in the nation, and boasts about attracting half a million spectators. The pyrotechnics are launched from five barges in the San Diego Bay, and this year's show – the 12th annual spectacle – was advertised by the port as being "bigger and more intense than in past years," and organizers set up free buses and shuttles to handle the crowds of spectators. About a dozen bayside hotels offer special Fourth of July rates just so customers can watch the show from the comfort of their rooms.

PHOTOS: Failures of 2012

The explosion was so bright and loud that some viewers initially thought the barges containing the fireworks had caught on fire. "Oh my God. Look at that. Is that supposed to happen?" said one person, whose comments were captured on a YouTube video. "I think a yacht blew up," @BENBALLER tweeted, along with a photo that appeared to show a breathtaking number of fireworks simultaneously exploding.