Dramatic footage posted on social media shows rivers of mud flowing through the town of Bitti in Nuoro province.
Italian media say the three who have died there include an older man who drowned at home and a man killed in his vehicle.
Strong winds and rain have battered the island since Friday, cutting off power and forcing some people to evacuate.
Several dams in Sardinia had to discharge water to avoid overflowing. The local authorities urged the residents of nearby settlements to avoid downstream areas. “The Preda and Othoni dam is discharging over 400 cubic meters per second,” one of the statements cited by the Italian media read, informing people that the roads in the area have been closed.
Some towns such as Villacidro located in the island’s south have been partially or completely isolated due to the floods and road closures. The recent events are reminiscent of Cyclone Cleopatra that hit Sardinia back in 2013 and claimed the lives of 18 people.