Japan is marking the first anniversary of a magnitude-9.0 earthquake and tsunami in the northeastern part of the country, which triggered the world's worst nuclear disaster since the 1986 Chernobyl accident.

More than 19,000 people died or went missing in the March 11 twin natural disasters, which also destroyed more than 370,000 houses.

At 05:46 GMT, the precise moment when the earthquake struck one year ago, a moment of silence was observed across the country.

Speaking at a ceremony in Tokyo, Yoshihiko Noda, Japan prime minister, pledged "to speed up ... the reconstruction of the affected areas " and to strengthen nationwide natural disaster measures. He also thanked the volunteers, both foreign and Japanese, who helped with the reconstruction work.

"Predecessors who led Japan's prosperity said that crisis is sometimes necessary in order to grow. We need to support the people who were affected by the earthquake and reconstruct Japan from this historic disaster. And that is my mission," he said.

Japan's Emperor Akihito also made a rare public address at the same ceremony, paying tribute to those lost and the volunteers who helped in rescue and rehabilitation efforts.

"These kind of activities gave hope and consolation to people who were forced to live very uncomfortable lives," he said.

"And at this opportunity, I would like to extend my gratitude to people who have been working for the affected people. Also I would like to pay my gratitude to those people who are working at the in the [Fukushima nuclear] power plant and overseas rescue teams, and many people have worked very hard to help us."