A powerful homemade bomb exploded outside a courthouse in the southern Italian city of Reggio Calabria, home to one of Italy's most feared crime groups, seriously damaging its entrance but causing no injuries.

Police sources said the device, composed of explosives on top of a gas canister, detonated in the early hours of today when there were no passersby.

Authorities are examining the remains of the bomb but so far have no theory as to who is responsible, the sources said.

The port of Reggio Calabria is one of the main cities of the southern region of Calabria, home to Italy's feared 'Ndrangheta organised crime group.