Mikhail Razvozhayev, governor of Sevastopol, the largest city in Russian-occupied Crimea, reported the incident on Telegram.
"An unidentified object flew into the courtyard of the Fleet Headquarters, according to preliminary data, it is a drone," Razvozhayev wrote.
The governor said six people had been wounded and that all planned festivities had been canceled due to "safety concerns."
"[Ukraine] decided to ruin Navy Day for us," he wrote.
The Odesa Military Administration's spokesperson Serhii Bratchuk denied that Ukraine was behind the attack, according to the Ukrainian outlet Euromaidan Press.