South Africa's President Jacob Zuma has been sworn into office for a second term, following his party's victory at the polls.
The African National Congress (ANC) won a commanding victory in the general election on 7 May.
More than 4,000 guests and several heads of state are at the ceremony in Pretoria.
Neither the US or UK are sending a representative but officials from Russia, China and India are attending.
President Zuma was officially elected for a second five-year term on Wednesday by the ANC-dominated parliament.
The expected formality of the re-election was disturbed only by MPs from the Economic Freedom Fighters (EFF), who turned up at parliament in red overalls and hardhats.
The EFF, led by former ANC member Julius Malema, said they dressed as maids and miners to show they intend to represent the interest of workers.
South African media say Saturday's inauguration ceremony is as much about celebrating Nelson Mandela, who died last year, and 20 years of democracy, as about officially sealing Mr Zuma's re-election.
Mr Zuma took the oath of office after prayers opened the ceremony at 11:00 local time (09:00 GMT).
Several heads of state are in attendance, including Zimbabwe's Robert Mugabe, Nigeria's Goodluck Jonathan, and Ugandan President Yoweri Museveni.
The US is not sending a representative but a White House statement said President Obama spoke to Mr Zuma on Friday to congratulate him on his re-election.
The centrepiece of the event was due to be a 90-minute cultural show, with performances from local musicians, dancers and a youth choir.
Proceedings are being broadcast at 45 public viewing sites across the country as well as being shown live on television and radio.
Members of the public descended on the Union Building in Pretoria, the site of the ceremony, to watch on large TV screens.
Mr Zuma will get back to work immediately after the national celebrations and is expected to announce his cabinet on Sunday.
His choices will be watched closely by political analysts with the country's economic problems continuing to mount and almost a quarter of all South Africans unemployed.