The aircraft, SG-401, which took off from Mumbai airport at around 5.30 am returned and landed safely at 6.05 am here.
"The pilot on board SG-401 observed the smoke alarm in the cargo hold. Following the standard safety procedures and checklists, the captain activated the fire extinguisher in the cargo hold and requested for priority landing," SpiceJet said in a release issued here.
The aircraft has been taken to an isolation area and investigating agencies like the Air Safety wing of the DGCA, the bomb detection and disposal squad, the Bureau of Civil Aviation Safety and airport fire agencies are inspecting the aircraft, it said.
The private airline said that all passengers have been deplaned safely and "We are making alternate arrangements to send the passengers to their destination with least delay."
Earlier, a Mumbai International Airport Limited (MIAL) official said all passengers were disembarked by 6.30 AM.