A 6.6 magnitude earthquake has struck off the eastern coast of Japan.

The US Geological Survey said the very shallow quake was centred 22km southwest of Iwaki, south of the stricken Fukushima nuclear plant.

The Pacific Tsunami Centre said the earthquake had not triggered a widespread tsunami.

Earlier, Japan fell silent as people across the country remembered the thousands killed by a 9.0 magnitude earthquake on 11 March and the monster tsunami it created.

It was also revealed today that the country will expand the evacuation zone around its Fukushima nuclear plant to areas beyond a 20km radius to include villages and towns that have seen increased accumulated radiation.

‘These regions could accumulate 20 millisieverts or more radiation over a period of a year,’ Japan's chief cabinet secretary Yukio Edano told a news conference, naming Iitate village, 40km from the plant, part of the city of Kawamata and other areas.

‘There is no need to evacuate immediately,’ he added, but said it would be desirable to proceed with the new evacuation over a one-month period.

Engineers working to prevent radiation leaking from the plant have said they are no closer to restoring the cooling system at the six reactors.

Almost 30,000 people died in the earthquake and tsunami that struck eastern Japan four weeks ago.

Japan urged to extend zone further

Japanese Prime Minister Naoto Kan told parliament last month that widening the area would force 130,000 people to move in addition to 70,000 already displaced.

The International Atomic Energy Agency had urged Japan to extend the zone and countries like the United States and Australia have advised citizens to stay 80km away from the plant.

The Japan Times said authorities would soon forcibly close the 20km zone, stopping people returning to their shattered homes to pick through the rubble for belongings.

The president of Tokyo Electric Power Co (TEPCO), which operates the Fukushima plant, planned to visit the area today, the first by Masatake Shimizu since the 11 March disaster.

Mr Shimizu has all but disappeared from public view apart from a brief apology shortly after the crisis began and has spent some of the time since in hospital.

Fukushima Governor Yuhei Sato was quoted by media as saying he would refuse to meet Mr Shimizu during his visit.

Mr Sato has criticised the evacuation policy, saying residents in a 20-30km radius were initially told to stay indoors and then advised to evacuate voluntarily.

‘Residents in the 20-30km radius were really confused about what to do.’ Mr Sato told NHK television on Sunday.

Engineers at the damaged Daiichi plant north of Tokyo said they were no closer to restoring the plant's cooling system which is critical if overheated fuel rods are to be cooled and the six reactors brought under control.

In a desperate move to cool highly radioactive fuel rods, operator TEPCO has pumped water onto reactors, some of which have experienced partial meltdown.

But the strategy has hindered moves to restore the plant's internal cooling system, critical to end the crisis, as engineers have had to focus on how to store 60,000 tonnes of contaminated water.

Engineers have been forced to pump low-level radioactive water, left by the tsunami, back into the sea in order to free up