Search and rescue operations were underway in Japan on Tuesday after Ishikawa Prefecture, in the Noto region along the Sea of Japan, was hit by a series of earthquakes on Monday.

The strongest quake logged a magnitude of 7.6, according to the US Geological Survey and other agencies.

At least 24 people were killed, officials said. Dozens more were injured.

"The search and rescue of those impacted by the quake is a battle against time," Prime Minister Fumio Kishida said during an emergency disaster meeting on Tuesday.

Tsunami warning and alerts

The Japan Meteorological Agency had issued a "major tsunami warning" for Ishikawa, while the rest of the northwestern coast of Japan's island of Honshu was issued lower-level tsunami warnings or advisories.

Public broadcaster NHK warned torrents of water could reach as high as 5 meters (16.5 feet), which is higher than the 3-meter threshold for a "major tsunami warning."

NHK reported that smaller tsunami waves had already been confirmed to have reached the coastline. 

The government said that as of Monday night, it had ordered more than 97,000 people in nine prefectures on Honshu to evacuate.

Authorities later downgraded the major tsunami warning to a "tsunami advisory," but people were still urged to move to higher ground. 

The country's meteorological agency warned that a 45-centimeter high (1.5 feet) tsunami on the South Korean east coast can grow and continue for more than a day.

The Hawaii-based Pacific Tsunami Warning Center, however, said later that "the tsunami threat has now largely passed."

Emergency services in the far eastern Russian island of Sakhalin issued an alert, saying that the island's western coast "may be affected by tsunami waves." 

North Korea also issued a tsunami warning. 

What do we know about the earthquake?

The Noto region saw a rapid succession of earthquakes, starting with a 5.7 magnitude tremor at around 4:06 p.m. local time (0704 UTC).

A 7.6-magnitude quake hit just four minutes later and was followed by a series of weaker tremors for around 90 minutes, said the JMA. In total, the agency recorded 21 quakes of 4.0 magnitude or higher. 

According to media reports, buildings swayed in the area around the capital, Tokyo, on the central coast of Honshu. 

Officials have warned that more earthquakes can hit the region over the coming days. 

"Residents need to stay on alert for further possible quakes and I urge people in areas where tsunamis are expected to evacuate as soon as possible," Prime Minister Fumio Kishida said.

Nuclear plants report no abnormalities

The Japanese government said no abnormalities were reported at the nuclear plant in the area and nearby stations.

Japan's Nuclear Regulation Authority said the Shika plant in Ishikawa, the closest to the quake's epicenter, had already halted its two reactors before the tremors for regular inspection.

Kishida said the government has set up a special emergency center to gather information on the quakes and tsunamis and relay them quickly to residents. 

A news conference was planned for 0910 UTC.

In 2011, a major quake and tsunami killed nearly 20,000 people, devastated towns and triggered nuclear meltdowns in Fukushima.

US support

President Joe Biden offered US help to Japan in the wake of the earthquake.

"As close allies, the United States and Japan share a deep bond of friendship that unites our people," Biden said in a statement.

"My administration is in touch with Japanese officials, and the United States stands ready to provide any necessary assistance for the Japanese people."

zc, jsi, mm, fb/kb (AFP, AP, Reuters)