Seismologists have warned that Japan may be hit by a “sizable” earthquake “any time in the future,” days after a 7.8-magnitude quake hit the country.

“We should be vigilant by knowing that it is no wonder that an earthquake sizable enough to affect our society can occur anytime in the future,” said Toshiyasu Nagao, the head of the Earthquake Prediction Research Center at Tokai University, on Sunday.

The Japanese seismologist made the remarks after the quake-prone nation was rocked by an earthquake measuring 7.8-magnitude on Saturday night.

The United States Geological Survey (USGS) said that the quake, which struck at a remote spot in the Pacific Ocean around 874 kilometers (542 miles) south of Tokyo, caused the buildings in the capital to sway for around a minute.

Twelve  people were injured in the earthquake, Japanese officials said on Sunday.

Toshiyasu, the Japanes seismologist, said, “I can say Japan is in an active stage now,” referring to recent quakes and volcano eruptions in the country.

Kazuki Koketsu, a professor with the Earthquake Research Institute at the University of Tokyo, however, said the quake on Saturday night does not necessarily preclude a potential big tremor in the capital.

He stressed, however, that “it is important to regard it as an opportunity to prepare for a future quake.”

Some experts have also warned that areas near Japan, which experiences around 20 percent of the world’s most powerful earthquakes every year, are entering “an active phase of crustal changes.”

Besides quakes, Japan, which lies at the junction of several tectonic plates, is also dotted with active volcanoes.

On Friday, the island of Kuchinoerabu on Japan’s remote southern region was hit by a five-minute-long volcanic earthquake, Japan’s Meteorological Agency said, adding that Mount Shindake on the island had shot black clouds reaching as high as 9,000 meters (29,500 feet) into the sky.

Sadayuki Kitagawa, the director of the volcanology division at the agency, said, “It’s possible that eruptions of a similar scale could happen in the future. We are warning residents about pyroclastic flows, and asking people to obey evacuation instructions.”

The volcanic earthquake forced the evacuation of the island.

IA/MKA/HJL