WASHINGTON - US President Barack Obama yesterday extended birthday wishes to Nelson Mandela, hailing SA's former president's "extraordinary vision, leadership, and spirit".

"On behalf of the United States, I wish Nelson Mandela a very happy 92nd birthday. We are grateful to continue to be blessed with his extraordinary vision, leadership and spirit," the US president said.

"We strive to build upon his example of tolerance, compassion and reconciliation," Obama added.

The greetings from America's first black president to South Africa's first black leader came as the world celebrated the first International Nelson Mandela Day in honour of Mandela's 92nd birthday, hailing his contribution to global politics and the fight for human rights.

"I also join the American people, the South African people, the United Nations and the world in celebrating the first annual International Nelson Mandela Day. I encourage us all to heed the call to engage in some form of service to others, in honour of the 67 years of sacrifice and service Madiba gave to us," Obama said.

"We strive to follow his example of what it means to truly give back to our communities, our nations and our world."

US Secretary of State Hillary Clinton also hailed Mandela.

"His story is filled with an amazing strength and integrity of spirit. There is no one more deserving of this unprecedented international recognition," Clinton said.

Said Martti Ahtisaari, former president of Finland: "(Former) president Mandela has given 67 years of his life, now what we all could do is try to use 67 minutes of our lives and change the world for the better."

Ahtisaari is a member of The Elders, an independent group of eminent global leaders formed by Mandela in 2008.