Updated at 11:09 a.m. ET Sunday
Defying a government ban, thousands of pro-democracy demonstrators returned to the streets of Hong Kong on Saturday and clashed with police throughout the night in one of the most dramatic and violent days of unrest since June, when the protests began.
The worst violence occurred at around 10 p.m. as riot police rushed into a metro station and arrested 40 people.
Riot police wielding batons pepper-sprayed bystanders and protesters inside Hong Kong's Prince Edward metro station before detaining incapacitated protesters. Video from inside the station showed metro passengers kneeling and begging for mercy as they were sprayed.
On Sunday, protestors blocked all roads, buses and metro lines to Hong Kong's airport but did not manage to shut it down. Riot police arrived early in the afternoon, causing hundreds of protestors and travelers to flee the airport, with many walking for hours to return to the city. Tung Chung, a metro station close to the airport, was temporarily suspended as riot police checked identification documents of passengers.
Events first took a violent turn on Saturday afternoon, when police fired tear gas and used water cannons laced with blue dye in their attempts to disperse protesters who were throwing objects and gasoline bombs at the main government headquarters.
One of the most striking images from Saturday's protests was that of a large fire, blazing across a street in a major shopping district. Protesters created a barricade of stadium chairs stretching across Hong Kong's Hennessy Road, close to police headquarters, and set it ablaze in the early evening.
A reporter heard at least three explosions as protesters threw Molotov cocktails at the blaze. Protesters also tore up patches of sidewalks for bricks to hurl at police headquarters. Masked demonstrators waving color-coded flags warned onlookers to stay a safe distance from the blaze, and firefighters were at the scene in minutes.
Riot police moved in quickly, causing protesters to move steadily eastward. Police began arresting protesters in Hong Kong's Wan Chai district shortly after, as jeering passersby and restaurant-goers shouted insults at law enforcement.
The day began peacefully with a "religious rally" — an attempt to evade the police restrictions around protests, though police still considered the event an illegal gathering.
Throughout the afternoon, protesters alternated between chanting for democratic elections and also singing religious songs. They said they were praying for peace — and also for "sinners." Marches then swelled into the tens of thousands throughout the afternoon as crowds moved peacefully west toward Beijing's government offices on Hong Kong island, which police began barricading that morning.
Saturday's demonstrations came on the fifth anniversary of Beijing's decision to continue vetting all candidates for Hong Kong's chief executive position. That decision sparked the 2014 "Umbrella Revolution," which consisted of months of mass pro-democracy protests but ultimately failed to secure direct elections for Hong Kong.
The past three months of protests in Hong Kong were triggered by legislation that would have allowed Hong Kong's government to extradite people to China for certain crimes — a proposal that critics feared could be used to target outspoken critics of China.
Though Hong Kong's chief executive, Carrie Lam, responded to protests by suspending the bill in mid-June, protesters continued to demonstrate because the bill has yet to be formally withdrawn. The activists have since expanded their list of demands to include calls for Lam's resignation, direct elections, an inquiry into police tactics and the unconditional release of all arrested protesters.
Lam has refused or ignored the demands. On Tuesday, Lam said the government was looking into all "legal means to stop violence and chaos" in Hong Kong. This past week, China sent additional troops to Hong Kong.
In a news conference Friday, Hong Kong police commander Kwok Pak Chung said unauthorized demonstrators could face jail sentences of up to five years.
Demonstrators showed up despite that warning — furious at what they see as police brutality, and further galvanized by a wave of arrests of prominent activists and politicians.
On Thursday and Friday, police arrested three prominent activists — most notably, 22-year-old Joshua Wong, who leads the youth activist group Demosisto. Wong was released on bail and attended Saturday's protests. Three pro-democracy lawmakers were also arrested on Friday, according multiple media reports.
Police in Hong Kong have made over 900 arrests associated with this summer's protests, but some see these targeted detentions as a shift in strategy. Man-kei Tam, director of Amnesty International Hong Kong, called the latest arrests and the ban on Saturday's rally "scare tactics straight out of Beijing's playbook."
Though police have targeted high-profile activists and pro-democracy thinkers, the protest movement in Hong Kong remains a leaderless movement.
On Sunday, protesters plan to shut down transportation lines into the Hong Kong International Airport for the third time in three months. On Monday, a general strike is set to begin across universities and many other sectors.
"I think when the government go hard, we go hard," said Isaac Cheng, a vice chairman of Demosisto. "We ask the government, please respond to the five demands as soon as possible. Otherwise, the people may be using some more radical ways or more hard ways to respond to the response of the government."