A Napoli fan was shot dead while more than 200 people were injured as title celebrations got out of hand in Naples, reports in Italy claim.
Luciano Spalletti's side claimed a first Scudetto title for 33 years after a 1-1 draw away from home against Udinese.
Napoli missed out on the chance to win the trophy at home to Salernitana, who scored a late equaliser to delay the party at the Estadio Diego Armando Maradona on Sunday.
But a Victor Osimhen equaliser at the Dacia Arena brought the point that Napoli needed to secure the league title on Thursday night and it sparked wild scenes in southern Italy.
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60,000 fans packed into the stadium to watch the clincher on big screens, while fireworks lit up the sky as others gathered in the streets of Naples to celebrate.
But things turned ugly, with reports stating a 26-year-old man was killed after being hit by a bullet fired from a gun in the Piazza Volturno area.
Italian outlet La Repubblica, via Sky News, say he was initially taken to hospital in a critical condition and later died.
Three others, a 26-year-old woman and two men, aged 20 and 24, also suffered gunshot wounds but their injuries are not believed to be life-threatening.
Police are now investigating the matter. Naples Prefect Claudio Palomba told RAI radio that the shooting had "nothing to do with the celebrations" and that only seven people were injured.
However, La Stampa claim the number of people admitted to hospital overnight is in fact more than 200 - with injuries varying from burns and asthma attacks caused by the firecrackers and flares, to knife wounds.
Beforehand, the US consulate issued a security alert ahead of the potential title celebrations, warning they could could carry on for "multiple days" and fearing "heavy traffic or road closures, significant use of fireworks, and alcohol consumption throughout the city."
Away fans in Udine invaded the pitch, while home supporters appeared with belts and batons as the riot police got involved.
Media in Italy say six fans suffered non-serious injuries in the fracas.
Josh Lawless