DHAKA: Tens of thousands of mourners are expected in Johannesburg for a memorial service for Nelson Mandela.

US President Barack Obama and the UN Secretary General Ban Ki-moon will be among those paying tribute, reports BBC.

The service will be held at the 90,000 capacity FNB stadium, where Mr Mandela made his last public appearance. It will also be shown on big screens at three "overflow" stadiums.

The former South African president died aged 95 last Thursday.

The country is observing a series of commemorations leading up to the funeral on Sunday.

The memorial service is likely to be one of the biggest gatherings of international dignitaries in recent years.

Hundreds of people began assembling outside the stadium during the night, the BBC`s Joe Winter reports from the scene.

Crowds, many wearing Nelson Mandela t-shirts and South African football and rugby tops, are singing songs from the fight against apartheid, our correspondent adds.

BDST: 1141 HRS, DEC 10, 2013