Orange County firefighters responded to a report of an explosion at a condominium complex at 1722 Mitchell Avenue shortly before noon Friday.
Two people were transported to UCI Medical Center in critical condition. The two men received "considerable, but non-life-threatening injuries," according to Tustin Police.
The Orange County Sheriff's Department confirmed a bomb squad was summoned to assist Tustin Police on scene.
The Orange County Fire Authority said the garage was a possible drug lab location.
Tustin Police said officers discovered what appeared to be a marijuana extraction lab in the garage. Officers found marijuana, several cans of butane gas and miscellaneous paraphernalia associated with a marijuana THC-extraction laboratory, police said.
About 10 to 15 pounds of marijuana were discovered inside the garage.
"It looks like they were trying to concentrate some of the marijuana oils out of the leaf," said Tustin Police Lt. Paul Garaven.
No further injuries were reported. Two other garages were damaged.