TOKYO (Kyodo) -- Some 65 percent of Japan's municipalities tapped to strengthen disaster preparedness said they were confused about how to respond to a Nankai Trough megaquake advisory issued for the first time this summer, a government survey showed Tuesday.

Among the 571 municipalities that responded, 13 percent admitted they were unaware of how the earthquake advisory system operated and were unsure of what actions to take, the survey by the Cabinet Office found.

In issuing the Nankai Trough megaquake advisory issued on Aug. 8, the first since the system's implementation in 2017, the central government urged increased disaster preparedness for a week while continuing daily activities.

But with fragmented responses from municipalities, including whether to proceed with planned events, it is now considering revising its guidelines for municipalities and businesses based on expert opinions.

Of 707 municipalities designated for enhanced disaster measures due to the expectation of strong shaking and large tsunami during a major quake, 80 percent responded to the survey on condition of anonymity.

When asked about specific steps taken following the advisory, 398 municipalities, or 70 percent, said they established disaster response headquarters, while 30 opened shelters, five issued evacuation orders and 37 decided to cancel or postpone events.

The 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.

The megaquake advisory in August was issued just hours after a M7.1 quake rocked southwestern Japan, with its focus located in waters off Miyazaki Prefecture, on the western edge of the Nankai Trough.