"It will not cost less than R100-million, it is costly," ANC national chair Baleka Mbete told reporters in Johannesburg.

"It is not cheap but we believe... it is worth it. Future and younger generations need to know where we come from."

The ANC was gathering archives and information about its history from around the world to be housed in one place.

"Some of the work is just priceless," Mbete said.

"Friends" of the ANC were coming forward and helping with funding.

About 120 000 people were expected to attend the main 100-year birthday celebration in Mangaung, in the Free State, in January next year.

"We are now, as of today, 60 days away from the anticipated January 8 celebration to commemorate the birth of the oldest and surviving liberation movement on the continent."

Mbete said the ANC had been preparing for the celebrations for the past two years. The main bash would start on January 6 and go on until January 8 2012.

It would start in Waaihoek, in the Western Cape, which was the founding place of the ANC 100 years ago, Mbete said.

The weekend would include an interfaith night vigil, an awards ceremony, a traditional cleansing and restoration ceremony, a presidential centennial gala and then the main celebration at the Mangaung rugby stadium.

ANC president Jacob Zuma was expected to deliver the centennial address at the stadium on January 8. Many international guests were also expected to attend.

"[They] will be given the opportunity to speak about their relationship with the ANC," said Mbete.

A number of African heads of state were coming, but Mbete said she could not give any more details.

The centenary celebrations would continue through 2012, with every month celebrating former ANC presidents.