It was later found out that these were the balloons released by the meteorology department, police said.
The pilot spotted the balloons when the plane was landing at Mumbai airport at around 11.00 am.
He alerted Air Traffic Control (ATC) room as well as Mumbai police control room.
Police conducted enquiry and found the met department had released the balloons to gather information about changes in the environment.
In view of terror attack threat fro air, flying balloons, drones and remote-operated aircraft is banned in Mumbai, police said.