Tsunami warning issued after earthquake off Fukushima, Japan

A 1.4 metre tsunami wave was recorded at Sendai, north-east of Tokyo, just over two hours after a magnitude 7.4 earthquake shook the Japanese island of Honshu early on Tuesday morning.

The epicentre of the earthquake, which was felt in Tokyo, was off the coast of Fukushima prefecture at a depth of about 10 kilometres at 5.59am. It sparked a tsunami warning for the Fukushima and Miyagi prefectures, with waves of up to three metres forecast.

The magnitude of the earthquake was initially reported at 7.3, however it was later upgraded to magnitude 7.4 by the Japan Meteorological Agency.

Just before 10am, local time, the agency said it was downgrading its tsunami warnings to the less severe "advisory" level.

"Slight sea-level changes may be observed in coastal regions, but no tsunami damage is expected," the agency said.

Earlier, Japanese authorities had told people in coastal areas of Fukushima and Miyagi prefectures to evacuate.

"Please stay evacuated and stay on alert," Japan's public broadcaster NHK said.

NHK showed a livestream of the coast around Fukushima, where the three-metre tsunami was expected to hit.

The 1.4 metre wave recorded at Sendai at 8.03am, is the largest to hit the region on Tuesday morning, after a series of smaller tsunami waves of between 30 and 80 centimetres were recorded along the coast.

NHK said the first report of a tsunami was observed about 20 kilometres off Fukushima's coastline, at 6.06am local time.

A series of tsunami waves have been observed along the coastline, including 80 centimetres waves at Kuji, Ishinomaki Ayukawa and Sendai, between 7.37am and 7.39am. At 7.06am local time, a wave of 90 centimetres was recorded at Soma.

At 6.49am, a 60-centimetre tsunami was observed at the Port of Onahama, at Iwaki, Fukushima.

NHK said back-wash has been reported at the port, as the sea level decreases for the approach of a tsunami.

The second and third waves of the tsunami were likely to be higher than the first wave, NHK reported. Tsunami waves may reach their maximum height a few hours or more after the initial wave.

The tsunami would hit repeatedly, NHK reported, and evacuated residents were warned not to return to coastal areas until the warning had been lifted. 

Evacuation orders issued 

Long lines of cars have formed as coastal residents follow government orders to flee to higher ground or an evacuation building.

NHK is repeatedly telling people in coastal areas of the Fukushima prefecture to evacuate to higher ground immediately.

"Please go to the higher ground right now. If there is no higher ground around you, please go up higher buildings, and please evacuate the seaside. Please inform your neighbours," NHK said.

A 1.4 metre tsunami wave was recorded at Sendai at 8.03am. Photo: JMA

Other areas of Japan's Pacific coast, including Aomori, Iwate, Miyagi, Ibaraki, Kujukuri, Sotobo and Chiba, have been issued with a tsunami advisory, with tsunami waves estimated to be between 0.2 and one metre.

There were no immediate reports of damage or injury.

Nuclear plants shutdown along the coast

All nuclear plants on the coast threatened by the tsunami were shut down in the wake of the March 2011 disaster, which knocked out Tokyo Electric Power Co's Fukushima Daiichi nuclear plant, spilling radiation into the air and sea.

A spokeswoman for Tokyo Electric Power, known as Tepco, said the cooling system for a storage pool for spent nuclear fuel at reactor at its Fukushima Daini Plant had been halted, but a spokesman said the cooling system had restarted soon after.

No other damage from the quake has been confirmed at any of its power plants, although there have been blackouts in some areas, the spokeswoman added.

Only two reactors are operating in Japan, both in the southwest of the country. Even when in shutdown nuclear plants need cooling systems operating to keep spent fuel cool.

Tohoku Electric Power Co said there was no damage to its Onagawa nuclear plant, while the Kyodo news agency reported there was no irregularities at the Tokai Daini nuclear plant in Ibaraki Prefecture.

Quake has 900 times less energy than devastating 2011 quake

Hugh Glanville, senior duty seismologist at GeoScience Australia, said his organisation estimates the quake to be of 7.1 magnitude, with revised depth of 15 kilometres.

First reports indicate a tsunami of 60 centimetres reaching nearby Iwaki Prefecture's shores.

"It's still considerable [in height] but often the following waves can be bigger," Mr Glanville said, noting tsunamis typically need a quake with a magnitude of 6.5 to be generated.

Early indications, though, put the quake at a much smaller size than the March 2011 monster of 9.1 magnitude.

"It's about 900 times less energy released and about 100 times less shaky," he said.

While quakes of Tuesday's magnitude can have variable impact of future quakes, this one may indicate a large quake is possible.

"It's quite a distance off the subjunction zone and quite shallow so it could be related to a fault that comes off the major plate boundary fault there," he said, adding that more information will be needed to be sure.

Still, "there is a higher likelihood of larger earthquake occurring in the immediate vicinity over the next 30 days or so," he added.

The region had a 6-magnitude temblor recently and another at magnitude 4.6 just under a day ago.

"There's lots of activity there all the time," with the Pacific and Eurasian plates colliding in the region, he said.

WATCH LIVE: ▶️https://t.co/awrxco46Zw pic.twitter.com/VtpNlOEOgt— Good Morning America (@GMA) November 21, 2016

Earthquakes are common in Japan, one of the world's most seismically active areas. Japan accounts for about 20 per cent of the world's earthquakes of magnitude 6 or greater.

Fukushima prefecture is north of Tokyo and home to the nuclear power plant that was destroyed by a huge tsunami following an offshore earthquake in March 2011.

The 2011 tsunami, sparked by a magnitude 9.1 quake, killed nearly 16,000 people with thousands still missing.