Cape Town: Desmond Tutu began his retirement Thursday on board a cruise ship in Cape Town, celebrating a career that earned a Nobel Peace Prize for battling apartheid and gave voice to South Africa's conscience.

Tutu announced in July that he would step down from public life on his 79th birthday, which he will ring in Thursday with his wife Leah on the 180-metre (590-foot) cruise ship carrying them on a five-month voyage around the globe.

"He's serious about quieting down," Tutu's spokesman Dan Vaughan told AFP. "He will now be refusing most of the interview requests he receives."

Tutu is currently lecturing on board the ship packed with 600 university students. Friends and family will join him later in the day in the harbour below Cape Town's landmark Table Mountain for a private birthday party.

Tutu served as archbishop for the Anglican Church in Cape Town, where he still lives when he's not travelling the world to speak out against injustice and encourage an end to conflicts.

His retirement has been greeted with doubt in South Africa that Tutu will actually step away from public life, with no coverage of his retirement in national media.

"He is going to be missed from public life most definitely. At the same time, one does understand there is a need for him to find some rest and respite after a life-long dedication and commitment to... change in South Africa," political analyst Chris Maroleng told AFP.

"Given his zeal and his determination, I wonder whether he'll really be able to fully retire as he has indicated."

Tutu says he will continue his work with The Elders, a group of leading statesmen that includes South Africa's first black president Nelson Mandela, and with a group of fellow Nobel laureates that encourages peaceful ends to conflicts.

He is also still working to develop the Desmond Tutu Peace Centre in Cape Town, where the organisation is building a new complex to house his peace projects.

Tutu won the Nobel Peace Prize in 1984 for his non-violent struggle against apartheid, establishing himself as the voice of the nation's conscience.

In the years since, he proved indefatigable in leading the Truth and Reconciliation Commission to uncover the horrors of apartheid-era abuses.

Tutu never shied away from shining a spotlight on modern South Africa's failings, while travelling the globe to promote efforts at peace from the Middle East to the Solomon Islands.

Last week he joined a group of international mediators in calling for outlawed Basque secessionists ETA to declare a permanent end to violence in Spain.

The archbishop works tirelessly with the United Nations to battle HIV and AIDS across the continent, and last month condemned the butchering of rhinoceroses in South Africa.

But Tutu increasingly appears to relish the notion of a simpler life.

"The time has now come to slow down, to sip Rooibos tea with my beloved wife in the afternoons, to watch cricket, to travel to visit my children and grandchildren, rather than to conferences and conventions and university campuses," he said in July.

Tutu also said he looked forward to having time to dote on his wife, Leah. They married in 1955 and have four children.

"Marrying Leah was the best decision I made in my life," he said in announcing his retirement. "Now I will have the time to serve her hot chocolate in bed in the mornings, as any doting husband should."