Japan and the US have issued tsunami warnings after a powerful magnitude 8.8 earthquake struck Russia on Wednesday.
Official evacuation orders have been issued to people on the Pacific coast of Japan and in Hawaii.
The first tsunami waves, at 30cm high, arrived in the northern coast of Japan's Hokkaido prefecture before 10.40 local time (02.40 BST), Japanese public broadcaster NHK reported. Waves at 40cm high have been observed in Tokachi, in Hokkaido.
US authorities have issued a tsunami warning for Hawaii, which warns it could face "destructive" 3-meter high waves. A tsunami watch has been issued for Alaska.
Waves 1-3 meters (3.3 to 10 feet) high could threaten the US island territory of Guam, according to the US Pacific Tsunami Warning Center, which is based in Honolulu. A tsunami is a series of powerful waves and can cause significant damage.
The earthquake magnitude was revised to 8.8 after an earlier measurement of 8.7.
The Japanese government has issued an evacuation order to people on the Pacific coast, saying: "Damage due to tsunami waves is expected. Evacuate immediately from coastal regions and riverside areas to a safer place such as high ground or an evacuation building.
"Tsunami waves are expected to hit repeatedly. Do not leave safe ground until the warning is lifted," it added.
Japan's Prime Minister Shigeru Ishiba said authorities were "working to access the situation", adding that any relief efforts will "put human lives first".
There was no confirmation of any damage so far, Ishiba said.
In Hawaii, officials ordered an "immediate evacuation" of large parts the island Oahu, including the state capital Honolulu.
"Take Action! Destructive tsunami waves are expected," Honolulu's Department of Emergency Management says in alerts on social media.
The US tsunami warning system has also issued tsunami advisory for California, Oregon and Washington states.
According to the US National Weather Service the first waves are expected to arrive at California at around 11.50pm local time (7.50am BST). Multiple waves are expected, lasting for 10 to 36 hours, it added.
Residents in California have received official SMS alerts warning them to avoid going to the coast and beaches, while stressing that there is no evacuation.
Speaking to the BBC's Newsday programme, Helen Janiszewski, Assistant Professor, Geophysics and Tectonics Division at the University of Hawaii said that the earthquake ranked among the ten most severe in recorded history.
According to the US Geological Survey, at magnitude 8.8 it was tied at the sixth most severe quake in history, with the 2010 earthquake in Biobío, Chile, and the 1906 earthquake in Esmeraldas, Ecuador.
A tsunami with a wave height of 3-4 meters was recorded in parts of Russia's Kamchatka Peninsula in its Far East, Russian officials said.
The tsunami warning was triggered by a powerful earthquake which struck about 126km (78 miles) from Petropavlovsk-Kamchatsky, Russia, at a depth of 18 kilometres, according to the United States Geological Survey.
In Russia, the tremor generated a tsunami of 3-4 metres in Kamchatka, according to Sergei Lebedev, the regional minister for emergency situations.
There were no injuries, but a kindergarten was damaged, according to preliminary information, Lebedev added.
"Today's earthquake was serious and the strongest in decades of tremors," Kamchatka Governor Vladimir Solodov said in a video posted on the Telegram messaging app.
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