A bomb exploded early Wednesday in a fire hose box on an elevated walkway in front of Kokusai-tenjijo Seimon Station on the Yurikamome Line in Koto Ward, Tokyo, police said.
No one was hurt in the 1:40 a.m. explosion at the station, which is the stop for the Tokyo International Exhibition Center, or Tokyo Big Sight, near the popular Odaiba waterfront area.
Police found wires and fragments of dry-cell batteries, as well as what appeared to be the remains of a timing device.
A security guard heard the explosion on the walkway that connects the station and the exhibition center, but he did not smell gas or gunpowder, police said.
Guards rushed to the site and found the stainless steel door of the hose box had been blown 6 meters away and the hose had fallen out.
Police said they are investigating the blast to determine if it is connected with an amateur comic book exhibition and sale that begins Aug. 9 at Tokyo Big Sight. They said a similar incident occurred at the center in August 1998 when another comic book sale and exhibition was being prepared.
In the 1998 incident, an explosive device was found in a cardboard box after a letter threatening to bomb the exhibition was sent to the organizers.