An earthquake with a preliminary magnitude of 6.8 rattled a group of Japanese islands in the Pacific Ocean south of Tokyo early Tuesday, Japan's weather agency said. No tsunami warning was issued.

The quake struck at about 6:18 a.m. (2318 GMT) and was centered near the Ogasawara island group, about 483 miles south of Tokyo, the Meteorological Agency said.

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The quake was extremely shallow, said agency official Toshiyuki Suzuki. There were no immediate reports of injuries or damage from the quake, he added.

Japan sits atop four tectonic plates and is one of the most earthquake-prone countries in the world.

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