An earthquake with a preliminary magnitude of 6.7 hit extensive areas centering on the Kanto region including Tokyo in the early hours of Thursday injuring six people, with an early warning failing to be issued in time. The six people in Tokyo, Ibaraki, Saitama and Chiba prefectures sustained minor injuries due to the 1:45 a.m. quake, according to the government's Fire and Disaster Management Agency. Smaller quakes were observed before and after that quake. The Japan Meteorological Agency's early warning system for major quakes, meanwhile, made an announcement 58 seconds after preliminary tremors were detected. Takashi Yokota, the head of the agency's Earthquake and Tsunami Observation Division, said the agency will study the feasibility of improving the methods to calculate magnitude because its initial underestimation of the 1:45 a.m. quake was behind the delay in the issuance of an early warning. The focus of the quake was around 40 kilometers below the surface of the sea in the Pacific off the coast of Ibaraki Prefecture.