Tsunami waves measuring up to 30 cm in height were observed on at least one of the Izu islands following a 6.6 magnitude earthquake in the western Pacific Ocean late Thursday morning.

The quake struck at 11 a.m. near Torishima in the Izu chain at a depth of 10 kilometers, with the Meteorological Agency issuing a tsunami advisory and originally forecasting waves of up to 1 meter for the remote chain of islands lying south of Tokyo.

The advisory has since been lifted.

People in coastal areas and near river mouths had been advised to retreat to higher ground.

“A 1-meter wave may not seem significant. ... But encountering such a wave can be extremely dangerous and it can sweep you off your feet,” a Meteorological Agency representative said at a news conference.

The tsunami was originally predicted to arrive along the Izu islands at various times, including at Hachijo-jima at 11:50 a.m. and Izu Oshima at noon. A 30 cm tsunami was reported to have been observed at Hachijo-jima (Yaene) at 12:17 p.m., although the agency said it could have been higher at other locations.

The meteorological agency warned of potential aftershocks, stating that there is a 10% to 20% chance of an earthquake with a similar magnitude occurring. It urged the public to be on alert for the next week.

According to the agency, seismic activity had been observed throughout the past week in the same area of the western Pacific Ocean beginning Monday and leading up to Thursday morning’s earthquake. Other quakes above magnitude 6 have also been observed in recent days.

So far, there has been no unusual volcanic activity as a result of Thursday’s earthquake, although cloud cover has made this difficult to confirm. Over the past week, aerial observations by the Japan Coast Guard have also shown no unusual activity.

The last time an earthquake of similar magnitude was observed near Torishima island was in 2006, causing a 16 cm tsunami to reach Miyake-jima. It is also the first time for a tsunami alert to be issued for the Izu islands since the 2022 Tonga-Hunga Ha’apai volcano eruption and tsunami.