However, there was no leakage outside the plant, said Trade and Industry Ministry official Yoshinori Moriyama.

The quake, which was followed by some 153 aftershocks, buckled many roads.

One highway was severed when a stretch of land collapsed, creating a cliff.

Electricity was cut to about 29,000 households, though service was mostly restored by last night.

'I couldn't do anything. I couldn't move,' said Ms Akiko Kikusawa, 82, who was among about a dozen people being served hot soup at an evacuation centre near Kurihara, one of the worst-hit cities in northern Miyagi prefecture.

'But I'm among the lucky ones,' she said. 'The other people here lost their homes.'

The meteorological agency issued a warning of a second quake four seconds after seismic waves were first detected, as Japan experimented with the world's first earthquake warning system.

A small window alerting residents opens on public broadcaster NHK's screen each time the agency issues a warning. Yesterday, it was flashed moments before residents of the capital felt a tremor.

Japan, where 20 per cent of the world's major quakes take place, developed the system largely to provide advance notice to nuclear power plants, railways and other infrastructure that can automatically shut down. It was launched in October last year.

AP, Reuters, AFP

Aftermath of Japan quake