Firefighters continued to tackle the blaze on Thursday. High temperatures and warm weather have contributed to the fire spreading.
According to both the police and public prosecutors, the fires are believed to have been the work of arsonists.
A suspect has already been arrested after being identified in video surveillance, La Repubblica reports.
The flames have destroyed hectares of land, including Cratere degli Astroni, a volcanic crater and nature reserve.
The area around Vesuvius has been nicknamed the land of fires, the Daily Beast reports, due to the illegal incinerators built by the Camorra crime syndicate. They are used to burn toxic waste and provide a profitable income stream for the mafia.
“If someone set fire to Vesuvius, I want to see them in jail for 15 years,”said Environment Minister Gian Luca Galletti.