As Nelson Mandela undergoes treatment for a lung infection after nearly a month in hospital, people continue to pay tribute to him, calling at an informal tribute wall to him near the hospital.

On Saturday, the Toronto Children's Chorus, who are on tour in South Africa, stopped outside the Medi-Clinic Heart Hospital in Pretoria to sing a New Zealand aboriginal song of blessing.

Wendy Hannam is a chaperone with the group.

"I think we will lose an incredibly gifted leader and the person who has had a huge impact in such a positive way on bringing this country together and in choosing a path of reconciliation when he came to power, to truly try to unite all people in the country. We will loose a great, great, great man."

Mandela is responding to treatment and the 94-year-old's condition remains critical, but stable after more than a month in the hospital, South Africa's President, Jacob Zuma said recently.

The anti-apartheid hero was admitted to hospital on June 8 for what the government said was a recurring lung infection, and his condition has been critical for over two weeks.

Mandela is well known for his 27 years of imprisonment under white ruled South Africa and his role in bringing reconciliation to the country after he became the country's first elected black president.

South Africa is preparing to celebrate Mandela's 95th birthday on July 18, which is also Nelson Mandela International Day.