Tokyo, April 20 -- A powerful earthquake with a magnitude of 7.5 struck northeastern and northern Japan on Monday, with a tsunami warning issued, the country's weather agency said.

An 80-centimeter tsunami was observed at Kuji port in Iwate Prefecture, the Japanese Met Agency said.

The 4:53 p.m. quake registered an upper 5 on the Japanese seismic intensity scale of 7 and occurred at a depth of 10 kilometers, according to the Japan Meteorological Agency, state media Kyodo cited.

"Notable quake, preliminary info: M 7.4 - 100 km ENE of Miyako, Japan," the USGS said. The earthquake's magnitude was initially estimated to be 7.4 but was later revised up.

The Japan Meteorological Agency has warned of quakes of a similar scale for a week, Kyo...