New York fire officials say fumes from two dozen bug bombs stored inside a Chinatown building sparked an explosion that injured a dozen people.

Three injured in the Thursday blaze remained in serious condition at hospitals Friday. Nine others were hurt, including four firefighters.

Fire officials said Friday that they believe two dozen pesticide canisters caused the blaze that started in the first-floor beauty salon. It was considered accidental. Officials are investigating reports that as many as 20 of the bombs had been set off at once.

The building had some open code violations and previous violations for rotting floors and unstable structure.

(AP)