VIDEO: 20 minutes of fireworks gone in 15 seconds

A glitch caused fireworks at San Diego's biggest display to ignite all at once, botching the Fourth of July pyrotechnic show for hundreds of thousands of spectators, the US media reported.

Fox 5 San Diego reported that viewers saw only a massive display of the Big Bay Boom shortly before 9pm on the day that marks American independence.

The Coast Guard was quoted as saying that a premature ignition occurred on several of the barges carrying the fireworks.

"I've never seen so many fireworks go off at one time," Rich Dann, a Coast Guard search-and-rescue controller, told reporters. "I saw what looked like a fireworks finale."

The Port of San Diego issued the following statement: “Approximately five minutes before the show was to start, a signal was sent to the barges that would set the timing for the rest of the show after the introduction.

“There were a number of preliminary test signals sent hours and minutes leading up to the show. All these signals tested properly according to Garden State Fireworks, the fireworks company that provides the show.

“The Garden State Fireworks team will be working throughout the night to determine what technical problem caused the entire show to be launched in about 15 seconds.

“We apologise for the brevity of the show and the technical difficulties.”