A gymnasium in Kasarvadavli area of Thane city was ransacked and set on fire on Sunday morning by unidentified persons, police said.
The incident happened at around 11:30am and the accused also disconnected the gymnasium's CCTV network and took away the digital video recorder, an official said.
"The fire brigade doused the blaze quickly. There are no reports of injuries but fitness equipment was destroyed. We are in the process of registering a case," he added.