As the 2021 Summer Olympics continue on in Tokyo, an undersea earthquake, considered "strong" on the Richter scale, has just struck off the eastern coastline of Japan’s main island of Honshu, followed by a few other notable tremors.

It hit at 5:33 a.m. on August 4 Tokyo time (1:33 p.m on August 3 Vancouver time), off the coast of Japan's Ibaraki Prefecture.

The Japan Meteorological Agency listed it as a 6.0-magnitude earthquake, followed a few minutes later by 4.7- and 5.6-magnitude temblors.

The U.S. Geological Survey measured it as a 5.8-magnitude seismic event, followed 10 minutes later by a 5.1-magnitude quake.

According to the U.S. Geological Survey, the epicentre, at a depth of 10 kilometres (six miles), was located 121 kilometres (75 miles) northeast of Hasaki; 131 kilometres (81 miles) east of Kashima-shi; and 137 kilometres (75 miles) northeast of Asahi.

No tsunami warnings or advisories have been issued.