A strong 6.1-magnitude earthquake rocked the northern Japanese island of Hokkaido Thursday but there were no immediate reports of damage, officials said.

There was no fear of a tsunami resulting from the quake which hit at 7:25 pm (1025 GMT), the Japan Meteorological Agency said.

The undersea tremor struck at a depth of about 30 kilometres (19 miles) in coastal waters off the southern tip of Hokkaido, the agency said.

Earlier Thursday, a moderate 5.9-magnitude earthquake struck close to the area hit by the massive March quake and tsunami, but there were no reports of damage.

The undersea quake hit at 4:24 am at a depth of 37 kilometres, 64 kilometres from Iwaki and 112 kilometres from Sendai, the US Geological Survey said.

Both cities were struck by the tsunami that left almost 20,000 dead or missing after a massive 9.0 earthquake in March.

The area is also close to a nuclear plant that was crippled by the double disasters and has since leaked radiation into the air, soil and sea, but has remained stable through a series of more recent tremors.