TOKYO (Kyodo) -- The chance of a megaquake occurring in the Nankai Trough within the next 30 years has increased to approximately 80 percent, the government's earthquake investigation panel said Wednesday.

Recalculations are made every January, taking into account the passage of time. The probability of a magnitude 8 to 9 quake along the trough in the Pacific had previously been estimated at 70 to 80 percent since 2018.

Noting that M6.0-level quakes have repeatedly occurred in Japan since the temblor on the Noto Peninsula, central Japan, on Jan. 1, 2024, the panel's chairman Naoshi Hirata, professor emeritus at the University of Tokyo, emphasized the need for continued vigilance as active seismic activity will likely continue for a while.

Such seismic activity has not been observed in Japan before, making "it difficult to predict when it might subside," Hirata said.

Earlier this week, the Japan Meteorological Agency issued its second-ever Nankai Trough Extra Information after an earthquake of magnitude of 6.6 struck southwestern Japan.

But while the jolting occurred beneath the western edge of the hypothesized epicenter of a Nankai Trough quake, the agency did not issue a special alert as it was not deemed to have immediately raised the risk of a megaquake.

On Aug. 8, 2024, the Japanese government issued a Nankai Trough quake advisory following an M7.1 quake that occurred off the coast of Miyazaki Prefecture, the first since the system's implementation in 2017.

Nankai Trough is an ocean-floor trench that runs along Japan's Pacific coast where the Eurasian and Philippine Sea tectonic plates meet.

Japan, a quake-prone nation, has long feared a magnitude 8 to 9 quake along the trough within 30 years, with predictions that a wide area could be jolted and vast coastal regions engulfed by massive tsunami.