Shortly before 6.00 am police received a tip-off from a passerby about a suspicious-looking canister in the area.
The device was found in an inner courtyard in Esterinportti, which houses a grocery and the Esteri restaurant.
On duty Lieutenant Heikki Kallio said it soon became apparent that there was no danger of an immediate explosion, so the police cordon was quickly lifted.
Lead investigator Markku Steinberg said the device was clearly a bomb, however he was not able to disclose further details.
Steinberg added that police will look more closely at the trigger mechanism and whether the device would have caused an explosion or a fire.
The case is being investigated as attempted sabotage. Police have not yet detained any suspects.