TOKYO: An 80-centimetre (31-inch) tsunami wave hit a port in northern Japan Monday after a powerful 7.4-magnitude earthquake struck the region, Japan's Meteorological Agency (JMA) said.
The wave was observed at 5:34 pm (0834 GMT) at a port in Kuji, Iwate, JMA said. It previously said a 70-centimetre wave had struck at 5:32 pm.
The quake hit at 4:53 pm (0753 GMT) in Pacific waters off northern Iwate prefecture and the tremor was strong enough to shake large buildings as far as Tokyo, hundreds of kilometres away.
The earliest tsunami waves could reach the northern shoreline immediately, the weather agency said.
"Evacuate immediately from coastal regions and riverside areas to a safer place such as high ground or an evacuation building," it said, warning that damage due to tsunami waves was expected.
"Tsunami waves are expected to hit repeatedly. Do not leave safe ground until the warning is lifted," it said.
Footage from national broadcaster NHK did not show any immediate visible damage around several ports in Iwate.
The prime minister's office said it had set up a crisis management team.
"For those of you who live in areas for which the warnings have been issued, please evacuate to higher, safer places such as higher ground," Prime Minister Sanae Takaichi told reporters, adding that the government was trying to confirm whether there were any casualties or property damage.
Japan is one of the world's most seismically active countries, sitting on top of four major tectonic plates along the western edge of the Pacific "Ring of Fire".
The archipelago, home to around 125 million people, typically experiences around 1,500 jolts every year and accounts for about 18 percent of the world's earthquakes.
The vast majority are mild, although the damage they cause varies according to their location and the depth below the Earth's surface at which they strike.
Japan is haunted by the memory of a massive 9.0-magnitude undersea quake in 2011, which triggered a tsunami that killed around 18,500 people and caused a devastating meltdown at the Fukushima nuclear plant.
In 2024, the JMA issued its first special advisory of a possible "megaquake" along the Nankai Trough.
This 800-kilometre undersea trench is where the Philippine Sea oceanic tectonic plate is "subducting" -- or slowly slipping -- underneath the continental plate that Japan sits atop.
The government has said a quake in the Nankai Trough and subsequent tsunami could kill as many as 298,000 people and cause up to $2 trillion in damage.
The JMA lifted the 2024 advisory after a week but it led to panic-buying of staples like rice and prompted holidaymakers to cancel hotel reservations.
It issued a week-long second "megaquake" advisory in December 2025 after a magnitude-7.5 tremor struck off the northern coast.
The December 8 quake triggered tsunami waves of up to 70 centimetres (28 inches) and injured more than 40 people, but no major damage was reported.