Zuma provided the update after visiting the 94-year-old anti-apartheid icon in the Pretoria hospital where he is being treated for a lung infection, CNN reported. Zuma said Mandela's doctors said the former president "remains critical but is now stable."
"He is much better today than he was when I saw him last night," Zuma said.
Mandela's oldest daughter said her father opens his eyes and responds to touch, the state-run South African Broadcasting Corp. reported.
"I reiterate that Tata [the Xhosa word for father] is very critical, that anything is imminent," Makaziwe Mandela said. "But I want to emphasize again that it's only God who knows when the time to go is. And so we will wait.
"He's ... still reactive to touch. We will live with that hope until the final end comes."
Mandela, considered the founding father of South Africa's multiracial democracy, has been hospitalized since June 8.
Authorities have described his condition as critical since Sunday.
Zuma canceled a visit to Mozambique, where he was supposed to attend a summit Thursday on infrastructure investment, so he could visit Mandela.
Mandela became a world figure while being imprisoned for 27 years for fighting apartheid, South Africa's system of racial segregation. He was elected the nation's first black president in 1994, four years after he was freed.
His administration focused on dismantling the legacy of apartheid through tackling institutionalized racism, poverty and inequality, and fostering racial reconciliation.
Mandela, whose birthday is July 18, received the Nobel Peace Prize in 1993.