Japan fell silent at 2:46 pm Monday as people across the country remembered the thousands killed by a 9.0 magnitude earthquake on March 11 and the monster tsunami it created.

In the devastated city of Kesennuma, soldiers digging through rubble to search for some of the 15,000 people still listed as missing stopped to pay their respects.

The minute’s silence followed a message from Japan’s prime minister who thanked the world for its support after the devastating disaster while the risk of a large radiation leak from a crippled nuclear plant began to fade.

Naoto Kan placed a signed open letter in some of the world’s leading newspapers thanking people for their help after massive waves following a huge earthquake on March 11 obliterated entire stretches of the northeast coast.

Around 13,000 people died and nearly 14,500 are still officially listed as missing in the worst tragedy to hit the country since World War II, which spawned the world’s worst nuclear disaster in a quarter of a century.

Kan’s three-quarter page announcement, entitled "Thank you for the Kizuna (bonds of friendship)," ran in international papers including the Financial Times, the Wall Street Journal and the International Herald Tribune.

As the letter appeared in the press, chief government spokesman Yukio Edano said the probability of a massive leak of radioactive materials from the Fukushima Daiichi plant was reducing.

Edano’s upbeat assessment was welcome news in a country used to hearing the worst from Fukushima, where only last week engineers plugged a hole out of which highly radioactive water had been spilling into the Pacific.

"The possibility that the situation at the nuclear plant will deteriorate and lead to new leakage of massive radioactive materials is becoming significantly smaller," said Edano.

"Obviously, the nuclear plant is not running normally. We have to continue to ask nearby residents to remain evacuated in case the situation deteriorates.

"We believe the risk of that has become significantly smaller compared to one or two weeks after the earthquake," Edano said, a month to the day after a huge earthquake and tsunami knocked out cooling systems at the Fukushima plant.

The government believed the current 20-kilometre (12-mile) exclusion zone was sufficient to protect people living near the plant against any sudden spike in radiation levels, he added.

Kan’s open letter, carried in newspapers in France, Russia, Singapore and China, among others, was a message of gratitude to governments, charities and individuals who have rallied to help Japan.

"One month has passed since an earthquake of unprecedented scale struck Japan, taking thousands of precious lives," the letter said.

"In the tsunami-devastated regions there was no cooking, no water, no electricity and the survivors had no communications.

"At that desperate time people from around the world rallied to our side bringing hope and inspiring courage.

"We deeply appreciate the Kizuna our friends around the world have shown and I want to thank every nation, entity and you personally from the bottom of my heart."

Many countries sent teams to help in the aftermath of the 9.0 magnitude quake and the huge tsunami.

For the 150,000 people still homeless, the one-month mark is just another depressing milestone.

One woman in her mid-30s who was rummaging through rubble in Rikuzentakata, a badly hit city where one in ten people is dead or missing, said the passage of time had brought no relief.

"A month on I am still searching for things. I want to be able to find even one photograph," she said.

"I am very worried about what I will do for work and about what’s going to happen in the future," said the woman, who did not want to be named.

Premier Kan Sunday made only his second trip to the disaster zone in the northeast, where hundreds of kilometres (miles) of coastline lie in ruins.

"The government will give all its strength to work with you. We will never abandon you," Kan told listeners to a radio station in hard-hit Ishinomaki city after witnessing the devastation.

Tokyo’s city governor, who was re-elected Sunday, said the city would bid for the 2020 Summer Olympics as part of efforts to boost recovery.