We are now closing our live coverage of the earthquake and tsunami response in northern Japan.

All tsunami warnings have been downgraded to advisories, with no remaining red warning zones in effect. 

Authorities say they will continue to monitor coastal conditions, but the immediate tsunami threat appears to have eased.

The magnitude-7.7 earthquake off the north-east coast triggered widespread evacuation orders affecting around 170,000 people.

Three injuries have been reported, according to NHK, but there are no reports of major damage or abnormalities at nuclear facilities.

Officials have urged continued caution in the days to come, citing the risk of aftershocks and further seismic activity.

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We've just received some positive updates: all tsunami warnings in northern Japan have now been downgraded to advisories.

An updated map shows no remaining red warning zones, with only yellow advisory areas still in effect along parts of the coast.

Airport operators in Shin-Chitose and Sendai say operations have not been affected, according to Japan's public broadcaster NHK.

Long tremors capable of rocking high-rise buildings have been recorded in Tohoku, at the northern end of Japan's Honshū island.

The Japan Meteorological Agency describes the phenomenon as "long-period ground motion," which primarily affects people on higher floors of buildings. 

It is measured on a four-level intensity scale.

Level 3 shaking — strong enough to make it difficult to remain standing — was felt in Wakuya Town in Miyagi Prefecture and Yokote City in Akita Prefecture.

Experts say such tremors can be powerful enough to topple furniture and cause disruption in high-rise structures.

The Japanese government says around 170,000 people have been told to evacuate since 6:45pm local time in areas affected by the earthquake and tsunami warnings off the northeast coast of Japan.

There are still no reports of damage and no abnormalities have been detected at nuclear plants.

Public broadcaster NHK reports that three people have been confirmed injured, after speaking to fire departments in affected zones.

Aerial vision shows waves crashing into the coastline of Hokkaido after a magnitude-7.7 earthquake struck off the north-eastern coast of Japan earlier tonight.

The Japan Meteorological Agency has revised the magnitude of the earthquake off Japan's northeast coast to 7.7 following further analysis.

The agency also updated the depth of the quake, saying it struck at 19 kilometres beneath the floor of the Pacific Ocean.

The Japan Meteorological Agency (JMA) says the estimated likelihood of a "megaquake" has risen from  0.1% to 1%. 

A spokesperson is urging people in tsunami warning and advisory zones to take disaster prevention measures over the next seven days.

A "megaquake" is an extremely powerful earthquake with a magnitude of 8.0 or higher, often occurring at subduction zones where one tectonic plate slips under another.

The Japan Meteorological Agency is holding another press conference. 

We're listening and will bring you key lines as they come.

Several bullet train services have been cancelled or delayed in northeastern Japan due to the earthquake and tsunami advisory.

The affected services include Tōhoku, Yamagata and Akita shinkansen lines.