An alert has been sounded and security tightened at railway stations, bus terminuses, entry points, vital installations, religious places and communally-sensitive areas of Mumbai after the explosion in Pune this afternoon, Deputy Police Commissioner Mahesh Patil said.
"I appeal to the people to inform the police if they spot any suspicious object and not believe in rumours," the DCP said.
Vehicles are being randomly checked by the police across the city, the police said.
The police are also checking hotels, lodges and boarding houses.
Hoteliers have been asked to make background checks of people renting rooms, the police said.
The Coast Guard and Navy are maintenance surveillance along the western coastline, using patrol vessels and helicopters.
Three people, including a constable, were injured when an explosive device kept in a motorcycle at a parking lot of Pharaskhana police station in Pune went off today, officials said.