SANTA ANA, Calif. (KABC) -- A Southwest 737 was forced to evacuate at John Wayne Airport after a fire broke out Monday night.The Southwest 737 was bound for San Jose but had not left the gate area when smoke was observed.The airline said flight 2123 was pushing back from the gate when the ground crew observed a possible fire near the rear exterior of the aircraft. The fire was in the aircraft's auxiliary power unit.The emergency slides were deployed and the plane's 139 passengers and five crew members were all evacuated safely and the fire was extinguished.The incident was first reported around 7:30 p.m. Orange County fire officials said the decision to evacuate the aircraft was made out of an abundance of caution."Although some ground crews had seen some smoke coming from the tail, which is where the auxiliary power unit is, the pilots had very quickly pulled the fire extinguishing system and if there was any fire back there, it was extinguished quickly," said OC Fire Authority Battalion Chief Ric Schultz.Five minor injuries were reported, but none requiring a hospital transport.Airline officials were working to get the passengers booked Monday night on another flight to San Jose.