A fire broke out Sunday at a five-story gymnasium at Hosei University in Tokyo, causing slight injuries to six students and a security guard, police and firefighters said.

The six students, aged 18 to 21 and all members of the women's basketball team, and the 37-year-old male security guard were taken to a local hospital and treated for smoke inhalation, the authorities said.

The fire started at around 11:30 a.m. on the 800-sq.-meter third floor, which sustained heavy damage, they said.

According to the authorities, the six students were practicing basketball on the fifth floor when the security guard told them of the fire.

The cause of the fire is under investigation, with inspections due to take place Monday.

Some 100 people were engaged in club activities in the gym when the fire started, the authorities said. The building has two basement floors in addition to the five above ground.

Investigations by police and firefighters showed that 10 students were practicing aikido on the third floor, which houses training areas for judo and karate students. Judo and karate club members were not practicing at the time.

The university is located in Chiyoda Ward, near Yasukuni Shrine.