PRETORIA (REUTERS) - South Africans have been coming in their hundreds to offer notes, flowers and prayers for Nelson Mandela at a wall surrounding a Pretoria hospital where the 94-year-old anti-apartheid hero remains in a critical condition.

Well-wishers' messages, bouquets and stuffed animals have piled up at the guarded boundary around the compound where doctors are treating the former South African president for a recurrent lung infection.

His health deteriorated at the weekend, bringing the sombre realisation for South Africa's 53 million people that the man who epitomised defiance of white minority rule and forged the post-apartheid "Rainbow Nation" may not be with them for ever.

A section of the beige brick wall has been plastered with notes of appreciation for his lifetime of struggle and sacrifice - including 27 years spent in apartheid jails - that helped lead to the country's first all race election in 1994.

"We know that the day will come when he passes but it is so painful to accept," said Ms Patricia Ndiniza, 53, an estate agent who left a note wishing Mandela a speedy recovery.

"He is a pillar for all of us. He is our pillar of peace and reconciliation," she said on Wednesday.

President Jacob Zuma has said doctors are doing their best to ensure the "recovery, well-being and comfort" of South Africa's first black president, one of the 20th Century's most influential figures.

President Zuma said on Wednesday that Mr Mandela's situation was unchanged. "As he remains in a critical condition in hospital, we must keep him and the family in our thoughts and prayers every minute," he told a meeting of a health workers union.

School children, prayer groups, office workers together with comrades and supporters who followed Mr Mandela in the anti-apartheid fight have trickled past the hospital day by day, passing a gauntlet of journalists and camera crews camped outside the main gate.

Fallen notes have been collected and replaced with new ones, some written in crayon by children and others penned by adults expressing their appreciation for Madiba, the clan name by which Mr Mandela is affectionately known.

Guards have propped up stuffed animals and placed flowers in water, lining them along the base of the wall.

"I left a bouquet. It wasn't much because it was all that I could afford," said Mr Tsepho Sibanyoni, who works as a driver.

"He's like Jesus for me. He has a golden hand. Mandela never took revenge for all of those who persecuted him but instead said, 'let us unite'," said Mr Sibanyoni 41.

Police have shut off streets to vehicle traffic near the hospital in the centre of the capital. The passage of pedestrians by the main gate grows at lunch and after normal working hours, with many stopping to reflect on the legacy of the political legend inside.

"This is a tough time to be a South African and an African, the old man was an icon," said passer-by Steven Makanamsa.

"When he does go, we must hold our hands together. We must be united. We must do something that is very important in our lives. That is what he taught us, what he wants," he added.

US President Barack Obama is due to visit South Africa this week as part of a three-country Africa tour. President Zuma said on Monday that Mr Mandela's worsening health would not affect the trip.

The public's last glimpse of Mr Mandela was a brief clip aired by state television in April during a visit to his home by Zuma and other leaders from the ruling African National Congress.

At the time, the 101-year-old liberation movement, which led the fight against white-minority rule, assured the public Mr Mandela was "in good shape", although the footage showed a thin and frail old man sitting expressionless in an armchair.