Men who appeared to be plainclothes security agents separated the two sides and led the protesters away, said John Hocevar, a member of the activist group, Students for a Free Tibet, who also videotaped the protest.
Separately, two protesters unfurled the Tibetan flag and chanted pro-democracy slogans among the spectators at the equestrian stadium in Hong Kong, but were removed and banned from the venue.
Earlier in the day, two protesters tried to unveil a Tibetan flag that was concealed behind a Canadian flag but security officers covered them with a piece of cloth before it was fully exposed.
At the Tiananmen protest, the protesters - three Americans, a Canadian and a German - "were calling for an end to the Chinese government's occupation in Tibet," said Lhadon Tethong, executive director of the New York-based group.
Tethong said four of the protesters wrapped themselves in the Tibetan national snow lion flag, which is banned in China, and lay down in a part of the square. Nearby, the famous portrait of Mao Zedong - Communist China's founding leader - overlooks that section.
The fifth stood by as the others were on the ground and told passers-by why they were protesting, she said.
While the demonstration was initially regarded with curiosity by onlookers, a group of young Chinese men suddenly started shouting "Get out! Get out!" and began surrounding them, the CBC footage showed. Some wore red and yellow headbands, China's national colors.
Confrontation over what is perceived as an insult to national pride by Chinese has become more common in recent months after protests by pro-Tibet groups and others during this spring's overseas Olympic torch relay.
Hocevar said he did not know where the protesters were taken.
Officials at the Beijing Public Security Bureau and Tiananmen Square police station would not comment.
Tethong identified Saturday's activists as Chris Schwartz of Montreal, Canada; Diane Gatterdam, Evan Silverman and Joan Roney from New York; and David Demes of Germany.
Earlier this week, Students for a Free Tibet held similar small protests, where they displayed Tibetan flags and hung pro-Tibet banners near the National Stadium, a key Olympics venue. Seven have been deported to Europe and the United States.
Over a half hour after the protest, Tiananmen Square appeared normal. Hundreds of tourists were at the famous tourist site.
Visitors are required to put their bags through security scanners before entering the square, scene of the 1989 pro-democracy student protests. Groups of guards stood under large umbrellas about every 50 feet, but they appeared relaxed.
Tibet has been an extremely sensitive topic since protests against almost 50 years of Chinese rule turned violent in the region's capital of Lhasa in March.
Many Tibetans insist they were an independent nation before Communist troops invaded in 1950, while Beijing says the Himalayan region has been part of its territory for centuries.
Pro-Tibet activists say China is using the sporting event to legitimize its rule in Tibet.