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 in diameter, has the emblem of the Japanese Olympic Committee branded on it.

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.