Japan's Meteorological Agency has issued its first-ever alert warning about a potential megaquake around the Nankai Trough, following a magnitude seven-point-one earthquake that struck off the coast of Kyushu earlier in the day.

According to Japan's public broadcaster NHK and the daily Asahi Shimbun on Friday, the Japanese government has immediately begun preparing response measures after the warning was issued.

Despite Thursday's quake leading to relatively minor damage of 12 injuries and collapse of two residential buildings, there is reportedly widespread concern among the Japanese people about the possibility of a megaquake around the Nankai Trough, which is known to occur every 100 to 150 years.

The Japanese government has estimated a 70 to 80 percent chance of a megaquake occurring within the next 30 years, spanning from waters off Shizuoka Prefecture, west of the capital region, to the eastern waters of Kyushu.

If such a quake were to occur, likely with a magnitude of 8 to 9, experts forecast that over 230-thousand people could be killed or go missing, and more than two-point-09 million buildings could collapse.

While the likelihood of a major quake in the Nankai Trough is currently higher than usual, the state agency clarified that the warning does not mean that an earthquake will occur within a specific timeframe. The current alert is expected to be in effect for one week.