Japanese Prime Minister Fumio Kishida on Friday canceled his planned four-day trip to Kazakhstan, Uzbekistan and Mongolia as the country's weather agency issued its first-ever alert over the risk of a possible Nankai Trough megaquake.

After attending a ceremony in Nagasaki marking the 79th anniversary of atomic bombing, Kishida told reporters that he canceled the trip to "focus on the government's response and information dissemination" regarding a potential megaquake.

The Japan Meteorological Agency (JMA) issued its Nankai Trough Earthquake Extra Information for the first time on Thursday evening, warning that the risk of a potential massive earthquake around the Nankai Trough that runs along the Pacific coast has increased.

The advisory does not recommend evacuation but calls for reviewing routine quake preparedness and staying alert for about a week.

The JMA issues such warnings when abnormal phenomena are observed along the Nankai Trough or when the possibility of an earthquake is believed to have increased, according to the Cabinet Office.

The Japanese government has previously said there is a 70 percent to 80 percent chance of a magnitude 8 to 9 quake occurring along the Nankai Trough within 30 years. Such a quake could lead to a tsunami of over 30 meters and, together, cause up to 320,000 deaths, according to a government estimate in 2012.

The first such advisory was released just hours after a magnitude-7.1 quake hit the country's southwestern prefecture of Miyazaki on Thursday afternoon.

Multiple injuries and damage to buildings have been reported in Miyazaki and two neighboring prefectures in the wake of Thursday's temblor, but no fatalities have been reported so far, local media reported.