The demonstrations were small - groups of no more than four people - and no arrests were reported.
The soft touch suggests Beijing might be hoping to repair its image abroad, which has taken a hit over hot-button issues like its human rights record and its policies in Tibet and Sudan.
But the rare public protests were quickly condemned by Olympics organizers, who are determined to make sure the communist government's plan for the Beijing Games goes off without a hitch.
"We express our strong opposition," Sun Weide, spokesman for the Beijing Olympics organizing committee, said after four pro-Tibet activists were led away by police after putting up banners on light poles outside the National Stadium.
Also known as the Bird's Nest, the stadium is where the opening ceremony for the games will be held Friday. It was the first protest at a games venue.
"In terms of assembly and demonstrations, China has related laws and regulations," Sun said. "We hope that foreigners will respect the related Chinese laws and regulations."
Those rules - stringent in normal times - have been tightened further for the Olympics. Beijing has said it would allow applications for public protests in three designated areas, but it's not clear if any had been accepted. None of Wednesday's protests were in the designated areas.
The government also has used its visa rules to try to keep out foreigners who might want to protest - former Olympic speedskater and Darfur campaigner Joey Cheek had his visa pulled Wednesday hours before he was to travel to Beijing.
The International Olympic Committee, which has faced criticism for giving the games to China despite its rights record, urged Chinese authorities to respond prudently to protesters.
Organizers should expect people to "use the platform of the Olympic Games to draw attention to their causes," said IOC spokeswoman Emmanuelle Moreau.
"The IOC are confident Beijing city authorities will assess the situation reasonably and act with tact and understanding," she said.
Later Wednesday, three Americans spent almost an hour in Beijing's Tiananmen Square criticizing the government's handling of issues ranging from forced abortions to the banned Falun Gong spiritual movement to pro-democracy demonstrations in 1989.
"It was important for us that there be a clear voice speaking out against the Chinese government's abuse of human rights," the Rev. Patrick Mahoney, director of the Christian Defense Coalition in Washington, told The Associated Press by telephone afterward.
The three erected a banner in front of communist strongman Mao Zedong's mausoleum that said "Christ is King" and knelt and prayed. Brandi Swindell, national director of the activist group Generation Life, put out seven roses in memory of those who died in the military crackdown on the Tiananmen protesters.
They said plainclothes security agents and police officers tried to block the banner with umbrellas and started shoving the group when they tried to walk around the square. The agents eventually pushed them out of the area and made them sit nearby for almost an hour, checking their passports, before letting them go, Mahoney and Swindell said.
Sun said the Tibet demonstrators were "persuaded to leave" by police, and were not detained.
Foreigners who protest Beijing's human rights record or official policy of atheism on Chinese soil would normally face deportation. Chinese who demonstrate would face detention and hours of questioning by police, at least.
Tibet has been an extremely sensitive topic since protests against almost 50 years of Chinese rule turned violent in the region in March, prompting a crackdown by security forces.
Also Wednesday, a documentary about Tibetans voicing opposition to the Olympics was screened for a few journalists at a small hotel near Tiananmen Square.
"If the 2008 Olympic games take place, then they should stand for freedom and peace. As a Tibetan, I have neither freedom nor peace. Therefore I don't want these games," said one unidentified monk who was interviewed for the 25-minute film.
The filmmakers said later that the hotel was shut down by authorities but a woman who answered the telephone at the front desk said she knew nothing about the screening and that business was normal.
At least one athlete promoted a political cause.
Amanda Beard, the Olympic 200-meter breaststroke champion, unveiled a poster of herself naked in support of the anti-fur activist group People for the Ethical Treatment of Animals. The launch has been planned for a hotel but happened outside the Athlete's Village after Chinese authorities canceled the hotel event.