Tens of thousands of protesters marched through central Hong Kong on Sunday wearing face masks in defiance of a law which bans them from hiding their faces.
Under the law, protesters risk a year in prison for wearing masks.
Protesters on Sunday chanted "Hong Kongers, revolt" and "Fight for freedom, stand with Hong Kong", as riot police monitored them from overhead walkways and footbridges, some taking photographs and filming the marchers.
Protesters handed out face masks to encourage people to defy the ban. One masked protester carried a mask-wearing "Buzz Lightyear" doll from Walt Disney Co's "Toy Story" animation film, Reuters reported.
Police fired tear gas in several places in the city but there were no obvious signs of clashes. Protesters ignored the gas, spreading gas canisters with water or throwing them back at police.
"Members of the public are advised to stay indoors and keep their windows shut," the police said in a statement.
Police said protesters were participating in unlawful assemblies, blocking major roads, and warned they would soon begin "dispersal operations on Hong Kong island". They ordered protesters to leave immediately.
Two major protests were planned on Sunday and authorities braced themselves, fearing a recurrence of Friday night's violent protests which saw Hong Kong's financial centre virtually shut down the next day.
Mask-wearing protesters took to the streets on Friday, setting subway stations on fire, smashing mainland China banks and clashing with police.
It happened only hours after Hong Kong's embattled leader Carrie Lam invoked emergency powers last used more than 50 years ago.
The emergency powers include a ban on masks at public demonstrations, which created an uproar.
"The anti-mask law just fuels our anger and more will people come on to the street," Lee, a university student wearing a blue mask, told Reuters on Sunday as he marched on Hong Kong island.
"We are not afraid of the new law, we will continue fighting. We will fight for righteousness. I put on the mask to tell the government that I'm not afraid of tyranny."
Hong Kong's four months of protests have plunged the Chinese-ruled city into its worst political crisis in decades. The pro-democracy movement poses the biggest popular challenge to Chinese President Xi Jinping since he came to power six years ago.
Protests started as opposition to a now-withdrawn extradition bill, but have evolved into a pro-democracy movement against what is seen as Beijing's increasing grip on the city which undermines its "one country, two systems" status promised when Britain handed Hong Kong back to China in 1997.
China dismisses the accusation and has claimed that foreign governments, including Britain and the United States, have fanned anti-China sentiment.
Friday night's "extreme violence" justified the use of the emergency law, Lam, who is backed by Beijing, said on Saturday.