An earthquake with a preliminary magnitude of 6.1 on the Richter scale struck Tokyo and its vicinity on Thursday, the Japan Meteorological Agency said, injuring nearly 20 people, with commuters left stranded and water supplies cut in some areas. However, there were no immediate reports of major damage. No tsunami warning was issued for the 10:41 p.m. (1341 GMT) quake. An operator of a nuclear plant in the affected area said there were no signs of abnormalities at the facilities. Shinkansen bullet train services between Tokyo and Shizuoka stations were suspended. The focus of the temblor was in Chiba Prefecture adjacent to Tokyo, at a depth of 80 km, the weather agency said. The quake measured upper 5 on the Japanese seismic scale of 7 in parts of Tokyo and Saitama Prefecture. The weather agency defines an intensity of upper 5 as strong enough to make most dishes in a cupboard and most books on a bookshelf fall. The Japanese scale measures how much places were shaken on the surface, while the Richter scale measures the energy of the quake itself. Japan is one of the world’s most earthquake-prone countries, accounting for about 20 percent of the world’s earthquakes of magnitude six or greater. Authorities were still investigating, but there were no immediate reports of damage or injuries in Chiba Prefecture or neighboring Saitama and Ibaraki prefectures, NHK reported. One woman in her 50s in Kanagawa Prefecture was injured when she fell and hit her head. Tokyo Electric Power Co. Holdings Inc. said that as of 11 p.m. about 250 households in the capital’s Shinjuku Ward were experiencing power outages.Some train lines were suspended and power was out in some areas following the quake, news reports said, while runways at Tokyo’s Haneda Airport were closed for safety checks. Officials were continuing to examine any impact from the earthquake. The last time a quake measuring upper 5 or more was registered in Tokyo’s 23 wards was on March 11, 2011, when a magnitude-9.0 quake devastated northeastern Japan and triggered a tsunami, the agency said. The agency warned that a quake of a similar intensity could occur within the week, with an official saying there was a 10 to 20 percent chance based on previous temblors. Prime Minister Fumio Kishida, whose government immediately set up a task force to respond to the quake, entered his office at around 11:20 p.m. He told reporters he had ordered officials to help quake victims and prevent further damage. There were many reports of burst pipes and water supply cuts in Tokyo, officials said. Japan’s top spokesman, Chief Cabinet Secretary Hirokazu Matsuno, said at a press conference that there were no abnormalities reported at nuclear facilities. The quake triggered a blackout affecting about 250 households in the Japanese capital around 11 p.m. but power was eventually restored. Railway companies said most subway services operated by Tokyo Metro Co. and some bullet train lines had resumed operation following the temblor. — Agencies