HONG KONG — This city’s subway system — spotless, efficient, cheap to ride — has been a source of civic pride since it began operating four decades ago, and it is often held up as a benchmark for public transportation everywhere.

When unrest began to grip Hong Kong early this summer, the Mass Transit Railway took on a different role. It carried protesters to demonstration venues, allowing them to leave the scene or shuttle between rallies in minutes. The spectacle of strangers clapping and cheering aboard trains and leading each other in chants replaced the usual sight of commuters hypnotized by their cellphones.

But as police crack down harder on dissent, station ticket halls and platforms are becoming battlegrounds, strewn with debris, tear-gas canisters and blood as officers clash violently with demonstrators.

Rail operator MTR Corp. also has become a protest target, stemming from a perception among demonstrators that it has conspired with authorities to stymie protest action. Stations have been vandalized so frequently in recent weeks that there is a shortage of parts needed for repairs, the rail union has said.

In a city where about 90 percent of journeys are via public transportation, the clashes have left some of Hong Kong’s 7.5 million residents feeling they no longer have any safe spaces, susceptible to arrest or police scrutiny whenever they venture out. Some people are boycotting the MTR, while others suffer flashbacks when they ride the trains.

“I am very afraid to take the MTR now, and bad thoughts always return to me when I pass by Prince Edward station,” said David, a 20-year-old student who watched police rush into train cars on Aug. 31 and swing their batons indiscriminately at protesters and civilians, leaving several injured.

“So many things happened there, and I can’t see this city as a safe place for me again,” added David, who did not provide his full name out of fear of reprisal.

The fallout has exposed a trust gap between protesters and Hong Kong’s government, which is not popularly elected and answers to Beijing.

Anyone “with any public authority has completely lost all confidence of [the] Hong Kong people,” Claudia Mo, a pro-democracy lawmaker, said at a news conference Wednesday. “It all stemmed from police brutality, which remains” unpunished, she added.

The protests began over a now-withdrawn bill to allow extraditions to mainland China, but they have grown into a wider battle to achieve full democracy for Hong Kong and to defend the semiautonomous territory against further encroachment by Beijing.

MTR, a public company that also runs malls and other real estate, appeared to shift its stance toward the protests after Chinese state media last month accused the rail company of aiding protesters by allowing them to ride home after demonstrations.

“The MTR presented a smiling face to the radical protesters and gave a cold eye to the police. With its actions, it has added to Hong Kong’s turmoil,” said an editorial in the Global Times, a nationalist newspaper that often reflects the views of the ruling Communist Party.

The language echoed a Chinese state media crusade against Cathay Pacific that eventually forced out the airline’s senior management and several employees who had voiced support for protesters. MTR Corp. denied buckling to pressure but began shutting stations around protest zones as a “prudent” measure.

Then came the Aug. 31 flash point. A largely peaceful march marking a milestone for Hong Kong’s pro-democracy movement ended with an elite police tactical unit entering subway cars at Prince Edward station, in the Kowloon district. Witnesses said officers used pepper spray and hit protesters with batons as they made arrests, requiring some to be taken away on stretchers.

“We appreciate that the MTR has had a great reputation, but everything has changed now,” said a 21-year-old student who would be identified only by her family name, Chan.

Police said they pursued only “radical” protesters at the Prince Edward station, adding that some had changed out of their signature black clothing to blend in with commuters. The force has rejected rumors of deaths that night as malicious smears.

Yet for many in Hong Kong, that night was another step too far by the police, whom protesters accuse of using disproportionate force. Hong Kong’s government has declined to meet a key demand from demonstrators to open an independent inquiry into the political crisis focusing on the police response.

On Tuesday, U.S. lawmakers introduced a bipartisan bill that would ban the sale of riot-control equipment, including tear gas, to Hong Kong police, fearing that the American-made gear is being “used to violently crack down on peaceful protesters.”

Since the August incident, protesters have targeted more MTR stations, smashing glass panels and spraying graffiti messages that accuse the corporation of colluding with the Chinese government.

At Po Lam, an outlying neighborhood, demonstrators confronted a station supervisor who later sought treatment in a hospital for minor injuries. On Sunday, protesters dumped trash cans and traffic cones down a stairwell at Central station and flooded the concourse with water. Some set an entrance ablaze.

The outpouring of anger has shocked MTR Corp., whose stock price has slumped 17 percent since mid-July.

In an open letter published Sunday, the rail operator’s chairman, Rex Auyeung, and its chief executive, Jacob Kam, acknowledged the network is facing “tremendous challenges.”

“At this crucial moment, we wish all sectors of the community could treasure and safeguard this railway network which has been carrying our collective memories over the past few decades,” they wrote.

On Monday, Hong Kong leader Carrie Lam toured Central station, inspecting graffiti on ticket machines and damage to turnstiles. Flanked by MTR executives, she wished injured staff a speedy recovery and thanked others for keeping the system operational.

At a news conference a day later, she focused her remarks on damage to the network and urged protesters to respect Hong Kong’s infrastructure. “I felt really upset after my inspection. No matter whether it is the Hong Kong International Airport or the MTR, they are both our lifelines,” Lam said.

Several protesters interviewed by The Washington Post said they believed that people had died in the Prince Edward melee, despite no conclusive evidence. Some residents have been leaving flowers at the station and performing Chinese burial rituals.

“We need the MTR Corporation to release all the CCTV videos and evidence related to August 31, but it still says no,” said 23-year-old Kin, giving only his first name. “I think among all the rubbish they’ve done, that’s the worst thing.”

Protesters are planning more boycotts of the MTR, urging each other not to shop in malls connected to the subway stops. Some plan a “sports day” — a euphemism for jumping turnstiles — for the coming week. Students even set up makeshift barricades to practice their jumps.

A 25-year-old woman who was on the platform at Prince Edward, returning from a movie theater when police rushed in, said she has avoided the station since and taken extra precautions to check her surroundings whenever she rides the train.

“You need to be ready for war at any time,” she said.

Timothy McLaughlin and Casey Quackenbush contributed to this report.