A strong undersea earthquake with a magnitude of 6.4 struck southeast of Tokyo on Friday morning, the U.S. Geological Survey said.

There was no tsunami warning issued by the Pacific Tsunami Warning Centre in Hawaii.

Japan's weather agency said there could be slight changes in the sea level but no damage to Japan.

The quake's epicentre was 226 kilometres southeast of the Japanese capital at a shallow depth of 10 kilometres, the USGS said.