Mandela 'very critical', says daughter NELSON Mandela's condition is "very critical" and "anything is imminent," his daughter Makaziwe Mandela says. "I can reiterate that Tata (father) is very critical, that anything is imminent, but I want to emphasise again that it is only God who knows when the time to go is," she told broadcaster SAFM on Thursday. The Nobel Peace Prize winner's health has deteriorated in recent days, prompting President Jacob Zuma late on Wednesday to pull out of a trip to neighbouring Mozambique - the first time he has scrapped a public engagement since Mandela was hospitalised on June 8. "President Zuma was briefed by the doctors who are still doing everything they can to ensure his well-being," a statement from the presidency said. On Thursday a large number of family members gathered at the Mediclinic Heart Hospital, along with the minister of defence, who is responsible for Mandela's treatment. Zuma was also seen returning to the facility. A few family members walked to the wall of messages and flowers where emotional crowds have been holding vigils, offering their prayers for one of the greatest figures of the 20th century. With his life seemingly slipping away, messages of support for the former president blanket the wall, including a poster bearing one of his most memorable quotes: "It only seems impossible until it's done." UN leader Ban Ki-moon said the whole world was praying for "one of the giants of the 20th century." "I know our thoughts and prayers are with Nelson Mandela, his family and loved ones, all South Africans and people across the world who have been inspired by his remarkable life and example," Ban said. Hillary Clinton offered "love and prayers to our great friend, Madiba, his family and his nation during this difficult time." The White House has also sent its wishes but could not yet say whether his ill health would affect a planned visit by US President Barack Obama to South Africa from Friday as part of a tour of Africa. Mandela's fragile state of health has sparked speculation that the tour could be halted, or radically changed, if the anti-apartheid icon passes away while Obama is on the continent. South Africa's foreign minister Maite Nkoana Mashabane has said that while Obama would have loved to see Mandela, a meeting with the former South African leader would be impossible.