Prime Minister Naoto Kan's right-hand man and top spokesman, Chief Cabinet Secretary Yukio Edano, earlier said: "it is believed that more than 1,000 people have lost their lives".

Amid a mass rescue effort there were grim updates indicating appalling loss of life along the hard-hit east coast of northern Honshu Island, where the monster waves destroyed more than 3,000 homes.

On Saturday afternoon, about 24 hours after the catastrophe, the National Police Agency said 503 people had been confirmed dead and 740 missing, with 1,040 injured in the disaster.

Police in Sendai, Miyagi prefecture, separately said Friday that at least 200 and up to 300 bodies had been found on the shore.

The defence ministry said about 1,800 homes in Minami Soma, Fukushima prefecture, were destroyed, while in Sendai authorities said 1,200 houses were toppled by the tsunami.

Thousands more homes were destroyed in a string of coastal towns -- including Ofunato, which on Friday reported 300 houses collapsed or swept away.

The monster quake was the strongest recorded in the seismically unstable archipelago, located on the "Pacific Rim of Fire".

In the quake-hit areas, 5.6 million households had no power Saturday and more than one million households were without water.

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