A strong earthquake with a preliminary magnitude of 6.8 has hit southwestern Japan, the country's Meteorological Agency said Monday. USGS

A strong earthquake with a magnitude of 6.8 has hit southwestern Japan, the country's Meteorological Agency said Monday, while warning the public to stay away from coastal areas because of a tsunami threat.

Tsunami advisories were issued for Miyazaki Prefecture, where the quake was centered, in the southwestern island of Kyushu, as well as nearby Kochi Prefecture, in Shikoku island, shortly after the quake struck at 9:19 p.m. local time, according to the agency.

There were no immediate reports of damage. Residents in some coastal areas were told to evacuate as a precautionary measure. One man was slightly injured in Kyushu after falling down some stairs, NHK reported. Trains stopped running in Miyazaki Station, stranding passengers.

Public broadcaster NHK TV said a tsunami, estimated to be as high as 3.2 feet high, reached land within 30 minutes of the quake. The waters detected at Miyazaki Port measured 8 inches high, the reports said.

The quake, centered at a depth of 30 kilometers (18.6 miles), shook a wide area in Kyushu, the southwestern main island, Japan's Meteorological Agency said.

The U.S. Geological Survey revised its estimate down from 6.9, adding that "there is no tsunami threat from this earthquake" for the United States.

The JMA nevertheless urged the public to stay away from coastal waters.

"Tsunami can strike repeatedly. Please do not enter the sea or go near coastal areas," the agency said on social media.

Japan is frequently hit by earthquakes because of its location along the "Ring of Fire," an arc of volcanoes and fault lines in the Pacific Basin.

NHK TV footage showed moving traffic and well-lit streets, meaning that electric power was still working. No problems were detected at the various monitoring posts for nuclear plants in the area.

Experts at the meteorological agency were meeting late Monday to gauge how the latest temblor may be related to the so-called Nankai Trough quakes.

The term refers to a wide region believed to be prone to periodic major quakes. A Nankai Trough quake off Shikoku in 1946 killed more than 1,300 people.

Last August, a powerful earthquake struck off southern Japan, causing mostly minor injuries but raising the level of concern over possible major quakes stemming from an undersea trough east of the coast.

An earthquake on Jan. 1, 2024 in Japan's north-central region of Noto left more than 240 people dead.

Japan has strict construction regulations intended to ensure buildings can withstand strong earthquakes, and routinely holds emergency drills to prepare for a major jolt.

But the country is haunted by the memory of a massive 9.0-magnitude undersea quake off northeastern Japan in March 2011, which triggered a tsunami that left around 18,500 people dead or missing.

The 2011 tsunami also sent three reactors into meltdown at the Fukushima nuclear plant, causing Japan's worst post-war disaster and the most serious nuclear accident since Chernobyl.

In March 2022, a 7.4-magnitude quake off the coast of Fukushima shook large areas of eastern Japan, killing three people.

The capital Tokyo was devastated by a huge earthquake just over a century ago in 1923.

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