Three reports of explosions or gunshots heard at underworld outposts here between late Wednesday night and early Thursday morning could be signs of yakuza warfare, according to police.

One report said a gunshot was heard coming from an office belonging to Nishimura-kai, an affiliate of the Yamaguchi-gumi crime syndicate, around 11:30 p.m. Wednesday. The office is located in a condominium complex in Hakata Ward.

At the condo, police found bulletproof windows shattered on the veranda, and a hole -- apparently caused by an explosion -- at the entrance.

Fifteen minutes later, in the town of Shime, the door of a car parked outside the home of Nishimura-kai boss Toshimi Nishimura was found damaged by an explosive, police said. A gun loaded with five bullets was found nearby.

Then at around 4:40 a.m. Thursday, a bullet hole was found in the door of an office in an affiliate of Dojin-kai, a crime syndicate also situated in the Hakata Ward condo complex, police said.