Major 7.5-magnitude quake hits off Japan, tsunami warning issued

A magnitude 7.5 earthquake struck off the northeastern coast of Japan on Monday, prompting authorities to urge residents to stay away from coastal areas where tsunami waves of up to 3 metres were expected.

Two hours after the tremor, which struck at 4:52 pm (0752 GMT), tsunami waves as high as 80 cm had been detected, though warnings remained for possible bigger waves at the top of Japan's main Honshu island, and the northern Hokkaido region.

There were no immediate reports of casualties or major damage, Japan's top government spokesperson Minoru Kihara told a news conference as night fell in the capital Tokyo.

Several port towns including Otsuchi and Kamaishi - both hard-hit by a massive earthquake and tsunami in 2011 - earlier issued evacuation orders for thousands of residents, according to public broadcaster NHK. Bullet train services were halted and some motorways were closed due to the tremors.

Big aftershocks may occur in the following days and weeks, an official from Japan's Meteorological Agency (JMA) said at a separate televised press conference.

NO ABNORMALITIES REPORTED AT IDLED NUCLEAR PLANTS

The quake measured an 'upper 5' on Japan's seismic intensity scale - strong enough to make it difficult for people to move around and cause un-reinforced concrete-block walls to collapse. The tremor had an epicentre in the Pacific Ocean and was 10 km deep, JMA said.

A 3-metre tsunami could cause damage to low-lying areas by flooding buildings and carrying off anybody exposed in its currents, according to JMA.

Located in the "Ring of Fire" of volcanoes and oceanic trenches partly encircling the Pacific Basin, Japan is one of the world's most earthquake-prone countries, with a tremor occurring at least every five minutes.

It accounts for about 20 per cent of the world's earthquakes of magnitude 6.0 or more, such as the 2011 disaster that caused nuclear meltdowns at a Fukushima power plant.

There are no nuclear power plants currently in operation in the affected areas and Hokkaido Electric Power Co and Tohoku Electric Power Co said there were no abnormalities reported at their idled facilities there.