A magnitude 5.7 earthquake struck central Japan in the early hours of Sunday, injuring more than 20 people, shattering shop windows and disrupting train services across a wide area around Aichi Prefecture. The Hindu BusinessLine, reporting from the Associated Press, put the number of injured at at least 22.

The Japan Meteorological Agency said the quake hit at 1:04 a.m. local time, centred in the western part of Shizuoka Prefecture at a depth of about 40 kilometres. The US Geological Survey measured the tremor slightly lower, at magnitude 5.5. No tsunami warning was issued.

The strongest shaking was recorded in Chita City in Aichi Prefecture, where the quake registered upper 5 on Japan's seven-level seismic intensity scale. That was the first shaking of that strength in Aichi since March 1997. Lower 5 shaking was also recorded in parts of Aichi, Shizuoka, Gifu and Nagano prefectures, and tremors were felt as far west as Osaka.

It was also the first time an earthquake in western Shizuoka Prefecture had produced upper 5 shaking since record-keeping began in 1919, according to the meteorological agency. Many of the injured were hurt falling on stairs or striking their heads as they fled buildings in the dark, and a woman broke her ankle while evacuating.

Services on the Tokaido Shinkansen, the high-speed line linking Tokyo and Osaka, were disrupted, and speed restrictions were imposed on expressways around Nagoya. No abnormalities were detected at the Hamaoka nuclear power plant in Shizuoka, according to its operator, Chubu Electric Power.

The meteorological agency warned residents to brace for further strong quakes over the coming week, especially in the next two to three days, and for a higher risk of landslides and falling rocks if rain hits shaken slopes. Officials assessed the likelihood that the tremor was linked to the feared Nankai Trough megaquake as low, while noting that the quake occurred inside the trough's projected source area.