The Japan Meteorological Agency continues to urge people to keep up their guard against a possible mega-quake in the Nankai Trough along the Pacific coast.

The agency on Saturday maintained its special advisory issued on Thursday after a magnitude 7.1 earthquake struck off Miyazaki Prefecture in southern Japan.

But agency officials say no irregular changes have been observed so far in the crustal strain.

The quake triggered tsunami that reached the coasts of the Kyushu and Shikoku regions. A 50-centimeter tsunami was observed at a port in Miyazaki City.

On land, the tremor registered a maximum intensity of lower 6 on the Japanese scale of 0 to 7 in Nichinan City.

Intensities of upper 5 were recorded in parts of Miyazaki and neighboring Kagoshima prefectures.

As of 2 p.m. Saturday, 16 perceptible jolts were observed in the region.

The meteorological agency is calling on people to stay on the alert as subsequent quakes with a maximum seismic intensity of lower 6 could strike over a period of roughly a week.

The agency says the probability of a major earthquake in the Nankai Trough is higher than usual. It issued the special advisory urging caution under what is known as the Nankai Trough Earthquake Extra Information protocol.

Agency officials say the advisory does not mean that a quake will definitely strike within a certain timeframe. But they have asked 707 municipalities in 29 prefectures -- extending from around Tokyo in the east to Okinawa in the south -- to check their disaster preparedness.

The government is advising people to secure furniture, and to check evacuation sites and ways to confirm the safety of their family members.

Households with infants, the elderly and people with disabilities are being advised to consider evacuating voluntarily.