An earthquake with an estimated magnitude of 4.4 rattled the Kanto region early Tuesday, temporarily disrupting train services on the JR Uchibo Line, the Meteorological Agency said.
There were no reports of casualties or damage from the 4:24 a.m. quake. No tsunami alert was issued.
The tremor registered 4 on the Japanese intensity scale to 7 in Tsurumi Ward, Yokohama, and Kisarazu, Chiba Prefecture; and 3 in Tokyo, Chiba and Kanagawa prefectures.
The quake's focus was 50 km beneath Tokyo Bay, the agency said.
A level 4 quake on the Japanese scale is strong enough to wake people.
The quake forced the cancellation of some trains and delayed others on the JR Uchibo Line due to a check of tracks between Kisarazu and Tateyama stations, railway officials said.
The predawn quake was followed by another at 6:10 a.m., which measured an identical magnitude of 4.4, the agency said. The quake registered 2 on the Japanese scale in Choshi, Chiba Prefecture, and several other locations in Chiba and Ibaraki prefectures.