South Africa has launched a special bi-metal R5 coin to mark the 90th birthday of former president Nelson Mandela.

The Nobel peace laureate is shown smiling and wearing one of his signature patterned shirts on the face of the coin, which was launched by the South African Reserve Bank, SA Mint Company and Nelson Mandela Foundation in Johannesburg on Monday.

"Today I am richer than yesterday," Mandela said at the unveiling.

The new coin will share Mandela's love, experience and leadership, said Finance Minister Trevor Manuel. "We are so privileged to have Madiba with us, who actively continues to provide leadership and who continues to be an example to all of us.

"The coin is in celebration of your birthday, but as a country we will be celebrating your life."

The coin is legal tender and should be used to purchase goods and services, Reserve Bank Governor Tito Mboweni said at the launch. "Do use it to buy goods and services, and do not keep it at home."

Five million of the coins have been minted and will go into circulation on Mandela's birthday on 18 July.

Other initiatives in celebration of his birthday include a colouring book, soon to be unveiled, which will give children the opportunity to give their own colour to his life.