The seabed tremor struck at 2:19 am local time (1719 GMT yesterday), jolting people out of bed as loudspeakers blared across the Ogasawara islands and authorities warned of the risk of a two-metre (six-foot) high local tsunami.

The tsunami alert was later downgraded and all warnings were lifted five hours after the quake hit near the islands, some 1,000 kilometres (600 miles) south of Tokyo. No injuries or damage were reported.

But about 120 people temporarily evacuated to higher ground on Chichi-shima island and some 50 people on Haha-shima island, Koji Watanabe, a village official on Chichi-shima, said overnight.

"It was the biggest earthquake I have ever felt," said Masae Nagai, a hotel owner on Chichi-shima, part of the remote archipelago also called the Bonin islands, which has a population of about 2,300.

"We were awakened by the quake. It was scary," she told AFP by telephone around sunrise, but she added that the walls of her hotel were not cracked and that "things have returned to normal".

Local authorities on the Ogasawara islands, near Iwo Jima, said they had set up five shelters for residents but had closed them before sunrise in the absence of damage reports.

"The jolts were relatively stronger than those we have felt in the past,"  Kenichi Mochida, another Chichi-shima official, told AFP. "But there was no panic as people acted in an orderly manner."

Yoshihiro Ikeda, vice principal of the Ogasawara Elementary School with 123 pupils in Chichi-shima, said, "We were worried about our students as the jolt was quite strong and lasted very long.

"But we were relieved to confirm that none of our students were injured and no facilities were damaged. I guess we were quite lucky, considering the size of the quake."
The quake hit at a shallow depth of 14 kilometres, 153 kilometres (95 miles) east of Chichi-shima, and was followed by a series of aftershocks measuring between 5.3 and 5.6 which continued into the morning.

About three hours after the quake, a 60 centimetre (two feet) wave was monitored 700 kilometres away at Hachijo-jima, part of the Izu island chain that runs south of Tokyo, the meteorological agency said.

Waves of up to 20 centimetres also reached the southwestern Japanese main islands, the agency said.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."

When a massive 8.8-magnitude quake, one of the most powerful on record, struck off Chile's coast in February, Japan issued its top tsunami alert and ordered more than half a million people to evacuate seaside areas.

Authorities later apologised after a wave of 120 centimetres hit and caused no injuries.
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.