Japan's Meteorological Agency has downgraded all tsunami warnings along the Sea of Japan to advisories.

The warnings were issued after a magnitude 7.6 earthquake struck Ishikawa Prefecture on Monday afternoon.

Even after the downgrade, the agency is urging residents to remain on the alert, as earthquakes of similar intensity will remain a possibility for about a week, and especially in the next two to three days.

The agency says tsunami advisories remain in effect for all prefectures along the Sea of Japan. Residents are urged to exercise caution.

Several cities in Ishikawa observed tsunamis. Wajima reported tsunami over 120 centimeters. Kanazawa recorded tsunami of 90 centimeters. Other prefectures reported sightings.

Tsunami are expected to repeatedly hit the coast and may become higher.

City officials in Wajima say a fire broke out in the center of the city.

Police say two people in the city of Nanao, Ishikawa Prefecture, suffered cardiac arrest following the quake.

NHK has learned from fire departments and hospitals that, as of 11 p.m. on Monday, people were injured in the prefectures of Ishikawa, Niigata, Fukui, Toyama and Gifu. They had reportedly been hit by items falling on them or had suffered broken bones.

Also in Wajima, the fire department says it has received more than 50 reports of collapsed houses. They are also responding to reports of people trapped under the damaged buildings. Officials are trying to grasp the full extent of the damage.

The Meteorological Agency says that following the 7.6 earthquake, it has observed more than 80 jolts in the region.

A hospital in Suzu, Ishikawa Prefecture reports it is treating patients injured in the earthquake. But some doctors have been unable to reach the hospital due to damaged roads. A hospital official says they are relying on a backup generator.

Medical staff at another hospital in Wajima have been treating patients in a parking area.

Reports of damage continue to come in.

In the neighboring prefecture of Toyama, police in the city of Himi say that they have received reports of cracks in roads at several locations.

A city official in Oyabe received several reports of broken water pipes.

Officials in Ishikawa's Nomi City say that at one point about 100 people were taking shelter in city hall.

Hokuriku Electric Power Company says it has shut down two generators at its Nanao Ota thermal power plant in Nanao City in Ishikawa Prefecture.

Officials say tens of thousands of households in Ishikawa, Niigata and Toyama prefectures are without power.

East Japan Railway Company says operations of the Akita Shinkansen line were suspended at around 5 p.m.

The Hokuriku Shinkansen and Joetsu Shinkansen lines have also partially halted service and will suspend some trains for the rest of the day. It is not known whether service will resume on Tuesday on the two lines.

The Nuclear Regulation Authority says a blast and the smell of something burning were observed at the Shika nuclear power plant in Ishikawa Prefecture.

The operator says functions using the transformer are currently unavailable.

But the plant operator says that the two nuclear reactors at the plant can function properly using alternative systems.

Japan's major telecom carriers say they are suffering service disruptions in the prefectures hit by the earthquakes.

Fixed-line carrier NTT West also says its internet and IP phone services may not be available in some areas of Ishikawa Prefecture. There are concerns that emergency phone services are also down.

Tsunami are also a risk in neighboring countries.

Weather authorities in South Korea say they have observed tsunami.

The authorities say further waves could come and last longer. The country's public broadcaster is urging people in coastal areas to evacuate to higher ground.

Meanwhile, authorities in Russia and North Korea have been urging residents to stay on the alert.