A 5.4-magnitude earthquake shook northern Japan on Saturday, the country's meteorological agency said, but there were no immediate reports of casualties or damage. The epicentre of the quake, which struck at around 9:35 am (0035 GMT), was 80 kilometres (50 miles) southeast of the city of Sapporo on Hokkaido island, the agency said. The quake struck at a depth of about 100 kilometres, it added. The US Geological Survey registered the quake's magnitude at 5.7, and said it struck at a shallow depth of just five kilometres. Around 20 percent of the world's most powerful earthquakes strike Japan.