They said they are trying to maintain public support for future protests.
"We want to protest in a peaceful manner and reduce the trouble created for all of Hong Kong's people," Louis Fung said as he handed out yellow flyers thanking people for their "consideration of any inconvenience caused."
About 100 demonstrators blocked the entry and lobby of the Inland Revenue Tower on Monday, the latest in a string of protests over fears that Hong Kong's legal autonomy is eroding. They then went to the nearby Immigration Tower, where they crowded escalators and blocked people waiting in line.
Some people trying to file tax returns shouted at the protesters, in some cases getting into shoving matches, though others were supportive.
Later, demonstrators discussed the backlash at an evening gathering and on online forums, and some decided to apologize.
Anna Ng, a college student, held up a sign outside the Immigration Tower reading "Excuse us for blocking everyone."
"I hope by employing more gentle strategies like this, people will be willing to understand us more," she said.
Hundreds of thousands of people have marched in Hong Kong in recent weeks to oppose legislation seen as increasing Beijing's control over the semi-autonomous city. Hong Kong's chief executive apologized and suspended debate on the bills.
Hong Kong has a separate legal system from the rest of China under an agreement struck before Beijing took back the former British colony in 1997. The legislation would have enabled some suspects to be extradited to stand trial in mainland China.
Protesters are demanding the total withdrawal of the legislation and an investigation into a harsh police crackdown at an earlier protest.
In recent days, they have been discussing how to push their demands and maintain momentum while keeping widespread support.
Sylvia So, a marketing worker whose walk to her office was disrupted by Monday's sit-in, said she supports the protests but was happy to see the activists apologizing.
"They are making a big step to let people understand what they are doing," she said.
Associated Press news assistant Nadia Lam contributed to this report.
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