Waves of 30 centimetres (one foot) hit the shores of the Ogasawara islands, an archipelago with a population of about 2,300 some 1,000 kilometres (600 miles) south of Tokyo, near Iwo Jima in the Pacific Ocean.

The tremor, which struck at 2:19 am local time (1719 GMT Tuesday), jolted people out of bed as loudspeakers blared across the island villages and national authorities warned of the risk of a two-metre high local tsunami.

But the meteorological agency downgraded the alert to a warning of a maximum half-metre (20 inch) wave following the quake and eight aftershocks measuring between 5.3 and 5.6 that started some 20 minutes later and continued throughout the night.

"The alert was downgraded but the village continues to advise residents to stay evacuated," Koji Watanabe, a village official on Chichi-shima, one of the Ogasawara islands, told AFP by telephone.

"About 120 people are evacuated to higher places on Chichi-shima island and some 50 people on Haha-shima island as of 3:30 am," the official said.

Asked about whether there were reports on any damage or injuries, he said: "I'm not aware of any injuries."

The quake hit at a shallow depth of 14 kilometres, 153 kilometres (95 miles) east of Chichi-shima.

NHK reported a wave of 30 centimetres hit Hachijojima island, part of the Izu island chain that runs south of Tokyo, at 4:01 am while the meteorological agency said a wave of 60 centimentres was reported at the island 90 minutes later.

The Ogasawara chain, made up of more than 30 subtropical and tropical islets some 240 kilometres north of Iwo Jima, were put under the control of the United States after World War II, and returned to Japan in 1968.

The remote islands have preserved their unique biological habitats and have been dubbed the "Galapagos of the Orient".

The Hawaii-based Pacific Tsunami Warning Center said after sounding the initial alert there was no threat of a destructive widespread tsunami and no nearby islands were thought to be in the tsunami danger zone.

But it warned in a bulletin shortly after the quake: "Earthquakes of this size sometimes generate local tsunamis that can be destructive along coasts located within 100 kilometres of the earthquake epicentre.

"Authorities in the region of the epicentre should be aware of this possibility and take appropriate action."

Around 20 percent of the world's most powerful earthquakes strike Japan, which sits on the "Ring of Fire" surrounding the Pacific Ocean.

In 1995 a magnitude-7.2 quake in the port city of Kobe killed 6,400 people.

But high building standards, regular drills and a sophisticated tsunami warning system mean that casualties are often minimal.

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