An earthquake with a preliminary magnitude of 7.4 jolted Ogasawara Islands in the Pacific early Wednesday, said the Japan Meteorological Agency (JMA), which issued a tsunami warning.

The focus of the quake, which occurred at 2:20 a.m. Wednesday ( 1720 GMT Tuesday), was located around 10 km under the sea off Chichijima in the Ogasawara island chain, some 1,000 km south of Tokyo, said the agency.

The offshore quake struck in the early morning hours at a depth of 10 kilometers causing a tsunami 60 centimeters high at Hachijo Island, located nearly 300 kilometers south of central Tokyo and a 30 centimeter tsunami was recorded at Chichijima about 1,000 km south of central Tokyo.

In addition, tsunamis of up to 20 centimeters were seen at Pacific coastal areas in Shizuoka, Mie, Wakayama and Kochi prefectures and the southwestern Japan islands of Tanegashima and Amami-Oshima in Kagoshima Prefecture, the Japan Meteorological Agency (JMA) said.

The agency later downgraded the tsunami alert to a warning and said only smaller waves of up to 45 centimeters were predicted. But the agency's seismology official Hirofumi Yokoyama said island residents should use caution for "several more hours" given the size of the quake's magnitude.

About 170 people evacuated to several community centers and school buildings on the Chichi and nearby Haha islands, the public broadcaster NHK said, although there have been no reports of damage or injuries.

At an early morning news conference, the JMA said that although there have not been active aftershocks, a M6-class quake triggering tsunamis of up to dozens of centimeters high could jolt the area in the coming week.

This is the second temblor registered Tuesday in the area known as the "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin. Earlier Tuesday, the U.S. Geological Survey reported a 5.7 magnitude earthquake off the coast in central Indonesia.

The agency highlighted the fact that Wednesday's earthquake was one of the largest quakes with an epicenter at a low depth since data become available in 1923.

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