The 25-year-old racer fell on the opening lap of the second race of the day, RIA Novosti reported.
"The motorcycle of a rider following the Italian hit him from behind," Superbike World Championship medical director Ruggiero Mattioli said on the event promoters' website.
"He was struck at the base of the skull. First aid was given immediately, after which Andrea was quickly moved to an ambulance, where he was intubated. Unfortunately, all these measures were unsuccessful."
The Russian news agency said video posted on the Internet showed the race was being run under wet conditions with plumes of spray reducing visibility.
Antonelli rode for Team Goeleven in the World Supersport category. He had raced internationally since 2005.
He is the first rider to die at a superbike event since British rider Craig Jones crashed at the Brands Hatch circuit in 2008.
The rest of Sunday's race program in Moscow was canceled.
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