TOKYO, Feb. 3 (Xinhua) -- The Japan Meteorological Agency (JMA) warned on Sunday that aftershocks may occur within a week after a strong earthquake jolted Japan's Hokkaido late Saturday, local media reported.
The JMA advised local residents to remain alert in the week ahead for aftershocks measuring up to about 4 on Japanese seismic intensity scale of 7, according to Japan's Kyodo News Agency.
The agency also revised the magnitude of the strong temblor hit Hokkaido to 6.5 from original 6.4 and the quake was marked about upper 5 on Japanese scale in some places in Hokkaido.
The JMA said it is unclear that whether the 6.5 magnitude earthquake has relations with the devastating quake in March, 2011.
The report also said that there was no serious damage at the affected areas after the quake, citing local authorities.
About a dozen of people suffered from minor injuries and some 840 households near the epicenter were temporarily without electricity, while some parts of highway were also closed briefly.
No abnormalities were found in nuclear plants in the affected areas, according to operators.