The Kowloon Tong station was seriously damaged in the attack, the government said in a statement. Riot police deployed in the streets of Kowloon and inside several metro stations afterward.
Hundreds of protesters, many young and wearing face masks, were marching in Kowloon at the time and were headed to a district near the Kowloon Tong station.
“No crime to cover our faces, no reason to enact (anti-mask) law,” protesters chanted. “I have the right to wear masks!”
The Hong Kong government introduced colonial-era emergency laws last week to ban the wearing of face masks at public rallies, a move that sparked some of the worst violence since the unrest started in June.
Some protesters erected road barricades using public garbage bins and water-filled plastic barriers used for traffic control and security.
Protesters elsewhere set fire to a government office in Kowloon and vandalised shops and metro stations, the government said.
There were no skirmishes between protesters and police and by nightfall protesters had dispersed into small groups scattered around Kowloon.
Hong Kong’s protests started in opposition to a now-abandoned extradition bill but have mushroomed in four months into a pro-democracy movement and an outlet for anger at social inequality in the city, an Asian financial hub.
The protests have plunged the city into its worst crisis since Britain handed it back to China in 1997 and is the biggest popular challenge to Chinese President Xi Jinping since he came to power in 2012.
The protests have been driven by a concern that China has been eroding Hong Kong’s freedoms, guaranteed under a “one country, two systems” formula introduced with the 1997 handover.
The now-withdrawn extradition bill, under which residents would have been sent to Communist-controlled mainland courts, was seen as the latest move to tighten control.
China denies the accusation and says foreign countries, including Britain and the United States, are fomenting unrest.
Hong Kong’s leader Carrie Lam cancelled a meeting with U.S. Senator Ted Cruz, the highest profile U.S. politician to visit the city since the unrest started, Cruz said on Saturday.
“I stand with the people of Hong Kong calling on the government of China to honour the promises it made to the world when it promised to maintain political freedom in Hong Kong,” said Cruz, a vocal critic of China, who was dressed in black in solidarity with pro-democracy activists.
Hong Kong’s police are also facing a crisis of confidence amid the worsening political tensions. Protesters accuse them of using excessive force, which police deny, and two protesters have been shot and wounded during skirmishes with police.
Hong Kong is facing its first recession in a decade due to the protests, with tourism and retail hardest hit.
Many shops have been shutting early to avoid becoming a target of protesters and due to closures of the damaged metro. Some stations on the network were closed on Saturday after being targeted.
Protesters have also targeted China banks and shops with perceived links to China, as well as U.S. coffee chain Starbucks (SBUX.O), which had a store in Kowloon trashed on Saturday.
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