A powerful 7.7-magnitude earthquake struck off northern Japan on Monday, prompting a brief tsunami alert and an advisory warning of a slightly elevated risk of a potential megaquake along coastal areas.

Japan’s Cabinet Office and the Japan Meteorological Agency said there is about a 1% chance of a megaquake occurring within the next week, compared with a normal probability of 0.1%, following the tremor near the Chishima and Japan trenches.

Officials stressed that the advisory is not a prediction but urged residents in 182 towns along the northeastern coast to remain alert, review evacuation plans and maintain preparedness while continuing daily activities.

Prime Minister Sanae Takaichi called on people to confirm designated shelters, evacuation routes and emergency supplies so they can respond quickly if needed. “The government will do our utmost in case of an emergency,” she said.

The quake, which struck off the Sanriku coast at around 4:53pm local time at a depth of about 19 kilometers, briefly triggered tsunami warnings. Waves of up to 80 centimeters were recorded at Kuji port and 40 centimeters at another port in Iwate prefecture before alerts were lifted.

Japan’s Fire and Disaster Management Agency said at least two people were injured after falling in Aomori and Iwate prefectures.

Shinkansen bullet train services between Tokyo and northern Japan were temporarily suspended, stranding passengers until operations resumed.

The Nuclear Regulation Authority said no abnormalities were detected at nuclear power plants in the affected areas.

The quake revived memories of the devastating 2011 Tōhoku earthquake and tsunami, which killed more than 22,000 people and triggered a nuclear crisis in Fukushima.