A strong earthquake rattled Japan's northern island of Hokkaido early Monday, US and Japanese meteorological agencies reported, the latest in a series of powerful tremors to hit the island nation.

The 6.2-magnitude quake struck at 5:23 am (2123 GMT Sunday) in Hokkaido's southern region, at a depth of 83 kilometres (52 miles), the Japanese Meteorological Agency reported, revising its preliminary estimate of magnitude 6.1.

No tsunami alert was issued, JMA said, and the US Geological Survey predicted that damage to property and threat to life was minimal, given the limited population in the region some 200 kilometres east of Sapporo.

But "in areas that experienced strong shaking, the danger of falling rocks and landslides has increased," a JMA official told reporters.

JMA also warned that risks of experiencing more quakes of a similar strength in the area in the coming week are high.

Hours earlier, a magnitude 5.0 earthquake occurred in the sea a few hundred kilometres south of Hokkaido.

The temblors come less than a week after the JMA warned of an increased risk of a megaquake -- 8.0 magnitude or stronger -- after last Monday's 7.7 earthquake off northern Iwate prefecture.

Six people were reported injured as a result of that quake, which shook large buildings in Tokyo, hundreds of kilometres from the epicentre.

In addition, 80-centimetre (31-inch) tsunami waves lashed a port in Iwate, while small waves also hit elsewhere in northern Japan.

Afterward, the JMA said "the likelihood of a new, huge earthquake occurring is relatively higher than during normal times".

Japan is one of the world's most seismically active countries, sitting on top of four major tectonic plates along the western edge of the Pacific "Ring of Fire".

The archipelago, home to around 125 million people, typically experiences around 1,500 jolts every year and accounts for about 18 percent of the world's earthquakes.

Japan is haunted by the memory of a massive 9.0 magnitude undersea quake in 2011, which triggered a tsunami that killed or left missing around 18,500 people and caused a devastating meltdown at the Fukushima nuclear plant.