By Belinda Goldsmith

BEIJING (Reuters) - Fake fireworks, a fake singer and now fake children at the Olympics opening ceremony.

Organisers of the Games acknowledged on Friday that children dressed in ethnic costumes from around China who carried the Chinese flag at the ceremony were not actually from those ethnic groups, some of whom have tense relations with the government.

This is the third faking incident to emerge from the Aug. 8 ceremony after it was revealed an angelic 9-year-old girl lip-synched the song "Ode to the Motherland" as the real singer was not pretty enough and some "live" fireworks 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."

But China's attempt to control every aspect of the ceremony, even if it meant some trickery and substitutions, and other manipulation at the Beijing Games such as bussing in cheering crowds has come under heavy criticism internationally.

"Rather than announcing China's arrival as a modern, dynamic country, they risk reinforcing the view that the Beijing government is comprised of control-freaks," said a commentary by British newspaper the Financial Times.

Media reports said the children were from the Galaxy Children's Art Troupe, which involves young actors and actresses mainly from the dominant Han ethnic group which makes up about 92 percent of China's 1.3 billion population.

But the programme for the 4-½ hour ceremony had said the children were from different ethnic 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.

On Friday pro-Tibet independence 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."

(For more stories visit our multimedia website "2008 Summer Olympics" at http://www.reuters.com/news/sports/2008olympics ; and see our blog at http://blogs.reuters.com/china)