Former South African president Nelson Mandela is "comfortable" in hospital, the country's leader Jacob Zuma has said.
President Zuma visited Mr Mandela at the hospital in Pretoria after the 94-year-old was airlifted to hospital on Saturday.
Mr Mandela is "comfortable and in good care," presidential spokesman Mac Maharaj said in a statement.
On Sunday morning worshippers gathered at the Regina Mundi Catholic church in the Soweto area of Johannesburg to pray for him.
The church was a centre of anti-apartheid protests and funerals.
"Yes, it really worries us because he is a great person," churchgoer Shainet Mnkomo said as she left an early morning service.
"He did so many things to the country, he's one of those persons who we remember most."
Mr Mandela, who spent 27 years in prison for fighting racist white rule, became South Africa's first black president in 1994 and served one five-year term.
He later retired from public life to live in his remote village of Qunu, in the Eastern Cape area, and last made a public appearance when his country hosted the 2010 World Cup soccer tournament.
Many in this country of 50 million people view Mr Mandela, who led the African National Congress to power, as a father figure and an icon of integrity and magnanimity amid the nation's increasingly messy politics.
Inside the church, a stained glass window depicts him, in a grey suit and blue tie, raising his hands to wave at a crowd.
His image stands next to another portraying a man carrying the corpse 13-year-old, Hector Pieterson, who was gunned down by police in the black township of Soweto in June, 1976, as students protested peacefully against the white government.
A statement from Mr Zuma's office announced that Mr Mandela had been admitted to hospital for tests and was receiving medical care "which is consistent for his age".
In February, Mr Mandela spent a night in a hospital for a minor diagnostic surgery to determine the cause of an abdominal complaint.
In January 2011 he was admitted to a Johannesburg hospital for what officials initially described as tests but what turned out to be an acute respiratory infection. He was discharged days later.
Mr Mandela contracted tuberculosis during his years in prison. He also had surgery for an enlarged prostate gland in 1985.