ANKARA

At least 50 people were injured in a powerful 7.5 magnitude earthquake that struck northeastern Japan late Monday night, with a warning of more tremors this week, local media reported Tuesday.

The majority of injuries were reported in the Aomori and Hokkaido prefectures, located along a major seismic trench where powerful earthquakes occur frequently as the Pacific Plate dives beneath the Honshu Island, according to Kyodo News.

The strong earthquake also prompted the suspension of ocean discharge of nuclear-contaminated wastewater from the crippled Fukushima Daiichi Nuclear Power Plant.

The quake's magnitude was initially recorded as 7.6 before being revised to 7.5.

Authorities warned that the region could experience another quake of similar or greater intensity in the coming days, and the government ordered thousands of residents to prepare for evacuation.

Defense Minister Shinjiro Koizumi said a military base in the city of Hachinohe in Aomori, the most severely hit, has been arranged as an evacuation center and hundreds of people were moved there.

At a municipal center in Hidaka city on the Pacific coast of Hokkaido, more than 200 people, including the elderly and young children, took refuge, as the temperature was minus 7.8C (around 18F) in the village on Tuesday morning.

For the first time, the Japan Meteorological Agency issued a special alert for the coastal areas of Hokkaido and the Sanriku coastline, which covers 182 municipalities in seven prefectures from Hokkaido to Chiba.

Following the quake, which occurred at around 11.15 pm local time on Monday (1415GMT), Tokyo issued tsunami warnings and advisories, urging people to seek shelter. However, the warnings were later lifted.

The earthquake was measured at a depth of 53.1 kilometers (nearly 33 miles) off the coast of the northern Aomori prefecture.

Prime Minister Sanae Takaichi urged residents to remain vigilant, follow updates from local officials, and take precautions such as securing unstable household items.

"The government asks residents to continue social and economic activities while maintaining a readiness to evacuate immediately if any shaking is felt," Takaichi told reporters.

Authorities also suspended schools in various areas, while transport and water supplies were also disrupted in Aomori and Hokkaido provinces after the earthquake.

Chief Cabinet Secretary Minoru Kihara said 31 of about 80 patients at a quake-damaged hospital in Mutsu, Aomori prefecture, were transported to nearby facilities.

The country's railway company JR East said it had suspended bullet train services on the Tohoku Shinkansen Line between Morioka in Iwate province and Shin-Aomori in the neighboring province of Aomori for inspections following the quake.

More than 10 moderate aftershocks, ranging from magnitude 5.0 to 6.6, were also reported in the hours following the main quake, according to the US Geological Survey.

Following the massive earthquake, tsunami warnings had been issued for prefectures Aomori, Iwate, and Hokkaido's Central Pacific Coast, with tsunami advisories for provinces Miyagi, Fukushima, and Hokkaido's West and East Pacific Coast.

The highest tsunami waves observed were 70 centimeters (nearly 27.5 inches) in Iwate.

Later, the warnings for all regions were downgraded to an advisory level, while the earthquake also caused power outages in about 2,700 homes in Aomori.

The government said around 1,360 homes in the Aomori and Iwate prefectures were also left without water due to damaged pipes.

No abnormalities have been reported by nuclear plants in Hokkaido or in the northeastern prefectures of Aomori, Miyagi, and Fukushima.

However, Tokyo Electric Power Company said that the discharge of nuclear-contaminated wastewater from the Fukushima Daiichi Nuclear Power Plant into the ocean was halted Monday night following the issuance of a tsunami warning, according to NHK.

While water also leaked from a spent fuel storage pool at a nuclear fuel reprocessing plant in Rokkasho, a Pacific coastal village in Aomori, it did not spread outside the building.