The 250-kilogram (550 pounds) bomb was found earlier this week in the bed of the Paglia River near the city of Orvieto in central Italy, the SkyTg24 broadcaster said.
Local authorities decided to proceed with the deactivation on November 20, declaring a safety zone of around one kilometer (0.6 mile) around the bomb. Around 2,400 people were evacuated from the area as a precaution early on Sunday. Rail traffic on the Rome-Florence high-speed line was also suspended.
Bomb technicians were supposed to complete the operation by 11 a.m. local time (10:00 GMT), but managed to transport the bomb to a quarry, where it will be blown up, nearly 90 minutes ahead of the schedule.
Road and rail traffic has been restored, with the evacuated residents returning to their homes, the broadcaster said.