This is the third faking incident to emerge from the ceremony after it was revealed an angelic nine-year-old girl lip-synched the song "Ode to the Motherland" as the real singer was not pretty enough and some "live" fireworks were pre-recorded.

Games vice president Wang Wei played down the latest incident, saying he did not know exactly where these children were from as they were performers representing China's 56 minority groups.

"It is typical for Chinese performers to wear different apparel from different ethnic groups. There is nothing special about it," Wang told reporters.

"They will wear different apparel to signify people are friendly and happy together."

The children were reportedly from the Galaxy Children's Art Troupe, which involves young actors and actresses mainly from the dominant Han minority which makes up about 92 per cent of China's 1.3 billion population.

But the programme for the 4-½ hour ceremony had said the children were from these groups.

"Fifty-six children from 56 Chinese ethnic groups cluster around the Chinese national flag, representing the 56 ethnic groups," read the media guide for the opening ceremony.

The fill-ins came as China struggles to keep conflicts with its ethnic groups out of the spotlight during the Olympics.

Human rights groups have tried to use the world's focus on the Olympics to highlight what they say is repression of Tibetans and Muslim Uighurs of Xinjiang by China's government.

Yesterday, pro-Tibetan campaigners staged a protest outside the state TV headquarters, the CCTV building, in Beijing.

"This is a very unwelcome and unacceptable action in China," said Wang, adding that most of the protesters were not Chinese.

"Tibet is part of China and the whole world recognise it. The free Tibet movement is not welcome here."