All of Japan's Olympic athletes have won "medals" even before they compete in London -- made of wood from debris found in the country's tsunami-ravaged northeast.

School children in the region carved pieces of the wood in the shape of an Olympic medal as good luck charms for the 518-strong Japanese Olympic delegation, which includes nearly 300 athletes.

Each unpainted medal, 4.5 centimetres (1.8 inches) in diameter, has the emblem of the Japanese Olympic Committee branded on it.

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Ribbons attached to the medals carry signed messages from the children including "Waiting for your medals" and "Bring back a lot of medals, please".

The wood medals were handed over at a send-off ceremony in Tokyo on Saturday, local media said, over a year after Japan was devastated by a quake-tsunami disaster which left about 19,000 people dead or missing.

Medal carver Mizuho Sato, 14, told reporters: "The debris had been a symbol of our sorrow but it has now taken on a new life."

The gesture brought 2009 world men's javelin bronze medallist Yukifumi Murakami to tears.

"I am really moved. I must repay what has been given to me," Murakami, 32, told reporters at the weekend.