Residents of Hong Kong, already tense after weeks of protests against the city's leader and police, were deeply shaken after masked assailants wearing white T-shirts savagely beat people dressed in black, the color of this summer's democracy movement.
The attackers descended late Sunday on an MTR rail station in the far northern district of Yuen Long, along the border with mainland China. Victims and rail riders uploaded dozens of videos that showed people bloodied and dazed.
One witness complained that police arrived after a half hour and allegedly left after 15 minutes.
Six were arrested, as police searched for the people responsible for the beatings of 45 people late Sunday night. The targeted victims included a lawmaker, journalists, and passersby. Businesses were so worried about further tensions that shops and malls remained closed.
Kaylee Lee, a registered nurse, retreated to a women's restroom at the station and treated wounded people with a physician. People kept pushing in to get away from the attackers.
"I couldn't believe what I was seeing," Lee said. "Some passengers were so injured, they couldn't walk by themselves. ... It was like a zombie movie. Some zombies wanted to get inside and attack us. We keep asking them to hold the door. Don't let them come inside."
As the government has been accused of ignoring demonstrators' demands, protests have grown angrier. Hours after Sunday's march, thousands of mostly young people wearing black clothing and construction helmets, joined rolling protests.
Participants threw black paint at the Chinese national emblem outside state offices, blocked off highways and built barricades from street signs.
By 2:30 Monday morning, all but a hundred or so protesters had left the unrest on Hong Kong Island.
Carrie Lam, the city's deeply unpopular chief executive, condemned the rail station attacks, but criticized protesters who defaced the national emblem on Beijing's liaison office.
"They blatantly challenged China's national sovereignty ... and angered the whole city," she said at a press conference.
Witnesses to Sunday's chaos faulted the police's slow and minimal response.
"The police really cooperated with the white-colored T-shirt people," said Mario, a bystander who asked that his last name be withheld out of fear that police might target him. "Why did the staff not do anything?" he asked.
Lam Cheuk Ting, a pro-democracy lawmaker who was bloodied in the event, said the attackers could be triad, or gang members, and said the police deliberately declined to act.
"It is a very serious misconduct in public office. It's an offense," he told journalists. "It's not just a disciplinary problem, but a criminal liability they have to bear."
A few people at the MTR station tried to hold off the attackers by spraying them with water hoses. In a video posted on his Facebook page, Lam and a few others appear to lead people up the stairs and onto an awaiting train. Downstairs, the concourse filled with several dozen masked assailants who ran up the station stairs chasing passengers. One lunged for Lam, while others beat and kicked other passengers.
The conductor left the train doors open, and minutes later, some of the attackers burst into the train carriage waving sticks. Some passengers beat them back with umbrellas. One passenger begged the assailants to stop but was punched so hard, he fell backwards. Another attacker lunged for Lam. With glasses in hand, he sat dazed, as blood poured from his mouth.
Bystander Mario said he tried to fend off the attackers with a fire hose, but escaped by slipping under the metal gate of a closing shop.
He was still furious on Monday.
"I don't know why suddenly there are no police in Yuen Long," Mario said. "Why would the government do that? Why did they allow people to attack lots of people?"
Protesters demand that an independent investigation be conducted into the forceful tactics used by police during previous demonstrations. Riot squads deployed tear gas, rubber bullets and bean bag rounds against mostly unarmed protesters, causing serious injuries.