BEIJING, Aug. 6 (Xinhua) -- With two days to go before the start of the Beijing Olympics, the organizers remain tightlipped about the details of the lighting of the cauldron at the opening ceremony and the identity of the last torch bearer.

"They are always the core secrets," Zhang Heping, director of the opening and closing ceremonies department of the Beijing Olympics Organizing Committee (BOCOG), told a press conference Wednesday.

But the organizers did offer some information about what are in stock for Friday's opening ceremony at the National Stadium, better known as the "Bird's Nest" for its giant latticework structure of metal girders.

"Chinese singer Liu Huan and British singer Sarah Brightman will jointly perform the theme song of the Beijing Games at the opening ceremony," said Zhang.

"It will be the first time that the theme song is presented to the public."

Liu Huan is one of the most renowned male pop singer in China, and Sara Brightman is a classical soprano, actress, songwriter and dance.

Zhang also denied speculations that a segment of the opening ceremony would be dedicated to the victims of the May 12 earthquake that hit south China's Sichuan Province.

"The earthquake is a catastrophe for the whole Chinese nation, but we believe the Olympic Games is a grand celebration of human beings and it should involve too many elements of sadness," said Zhang.

All 205 National Olympic Committees affiliated to the International Olympic Committee will take part in the Beijing Games, marking a union of the Olympic family.

Zhua said that the marching order of the 205 National Olympic Committees at the opening ceremony is being dictated by the number of Chinese strokes in the first syllable of each NOC in Mandarin.

The opening ceremony is due to run from 8 p.m. to 11:30 p.m. local time.