Security staff moved in as soon as the pair tried to display the Tibetan flag
A student who tried to unveil a Tibetan flag during the first day of Olympic competition has been removed by officials from an equestrian event.
Christina Chan tried to display the flag, hidden under a Canadian flag, at the dressage in Hong Kong.
She was asked to leave, but refused to do so, and was later removed from the arena with a second protester.
The Games opened in Beijing on Friday with a spectacular display of fireworks, music and dancing.
Some 10,000 performers took part in the ceremony, watched on TV by an estimated one billion people, before athletes paraded around the national stadium.
Security was tight in the capital, and three US activists were arrested after holding a pro-Tibet protest.
Ms Chan sat in the front row of the dressage arena in the Sha Tin district of Hong Kong, when the first full day of the Games got under way.
Christina Chan refused to leave and was later removed
She was holding a Tibetan flag concealed under a Canadian flag, and when she and another protester tried to display it, several security officials covered her with a blue cloth.
She was asked to leave, but refused to do so, and was later carried out of the venue.
"She was sort of disturbing other spectators around her, which is against the house rules," equestrian event spokesman Mark Pinkstone said.
Ms Chan had also protested during the Hong Kong leg of the Olympic torch relay in May.
China bans the Tibetan flag from events under rules which prevent the display of flags of countries not competing in the Games.
Anti-government riots broke out in the Tibetan capital Lhasa and elsewhere in China in March.
Pro-Tibet groups say there have been many arrests and beatings in the security crackdown which followed.