HONG KONG — The death of a Hong Kong student Friday following a police operation unleashed a wave of anger and heralded a new phase in five months of confrontations between authorities and demonstrators calling for democracy in the semiautonomous Chinese territory.

Thousands assembled for spontaneous vigils throughout the city, and by nightfall the gatherings had devolved into confrontations with police, with protesters building road blockades, hurling bricks and starting fires.

Police used tear gas to disperse protesters in multiple neighborhoods and fired a live round into the air as a warning shot in the neighborhood of Yau Ma Tei, police confirmed in a statement.

At least seven pro-democracy lawmakers were reportedly arrested or summoned for “arrest by appointment,” according to local media. The development set an ominous tone for upcoming district elections at the end of the month — contests from which prominent pro-democracy activist Joshua Wong has already been barred.

Chow Tsz-lok, a computer science student at the Hong Kong University of Science and Technology, had been in a coma since early Monday, when he fell one story in a parking garage in the Tseung Kwan O neighborhood while police officers were dispersing protesters nearby. The 22-year-old died shortly after 8 a.m. Friday, hospital officials said.

Graduates from a Hong Kong university were in mourning Nov. 8 after they heard news that a student had died amid the city's unrest. (Reuters)

Chow’s death could be the first directly connected to a police confrontation with protesters, but the details of what exactly happened in the lead-up to the fall are not clear. Security footage released by the building owner on Wednesday did not capture the moment Chow fell. Local reports have said that he was about 130 yards from police officers, who had fired tear gas to clear protesters in the area.

The fatality quickly ignited the city’s pro-democracy movement. By Friday afternoon, crowds of black-clad people began gathering across the city to commemorate Chow’s death. Marchers bearing white flowers brandished signs denouncing the police and calling for revenge. Traffic came to a standstill as demonstrators occupied roads in central Hong Kong, chanting “Five demands, not one less!” — a motto of the protest movement.

Several more vigils and memorials were held throughout the city on Friday night. Hundreds of mourners, some carrying origami cranes, lined up to pay tribute to Chow at the parking garage where he fell to his death. As attendees poured out of the packed building and onto the streets, crowds chanted, “Free Hong Kong! Revolution of our times!” On a balcony, protesters lit candles and unfurled a “Never Forget” banner.

“I’m really sad. He shouldn’t have died,” said a 24-year-old analyst in the crowd, who asked to be identified only as K for fear of retribution. “There’s a lot of sadness going on right now. We don’t want anyone to die.”

Some protesters have alleged that Chow was fleeing from police when he fell, and they accused officers of obstructing medical responders who were trying to reach him. Police have denied interfering in the emergency response.

“We all are very angry, devastated and frustrated,” said Percy, a 20-year-old medical student who volunteers as a first-aid responder and who declined to give his full name, for fear of retribution from authorities. “The police [are] shameless that they claim they didn’t delay the ambulance or they didn’t do anything that led to this accident.”

In a statement, the Hong Kong government expressed “great sorrow and regret” over Chow’s death.It added that the police “attach great importance to the incident and the crime unit is now conducting a comprehensive investigation with a view to finding out what happened.”

Public anger has grown as Hong Kong authorities, encouraged by Chinese officials and state media, have deployed increasingly forceful tactics to try to quell the anti-government unrest. Police have fired nearly 6,000 containers of tear gas, along with rubber bullets and, on occasion, live ammunition. About 3,300 people have been arrested. Carrie Lam, Hong Kong’s leader, has refused to authorize an independent inquiry into police actions, a key demand of protesters.

On Friday, citing new video footage, police revised their initial time frame of events on the night that Chow fell in the parking garage.

With the city on edge ahead of more demonstrations expected later Friday and through the weekend, police also warned of “radical comments made online.”

“We appeal to members of the public to stay calm and rational,” Suzette Foo, senior superintendent of Kowloon East Region, told reporters.

Hong Kong’s protests erupted in June over a now-withdrawn bill to allow extraditions to mainland China, but they have morphed into a broader uprising against Chinese government encroachment into the city’s affairs. The intensifying police crackdown has eroded support for the city’s Beijing-backed leadership, which many here perceive as working with the Chinese government to undermine Hong Kong’s political freedoms, autonomy and the rule of law.

At the same time, front-line protesters have adopted more violent tactics. Some have vandalized businesses, including mainland banks and Hong Kong’s subway operator, that protesters view as supporting the Chinese government.

On Friday, the second day of college graduation ceremonies, Wei Shyy, president of the Hong Kong University of Science and Technology, made a tearful announcement of Chow’s death to an audience of graduates, some wearing black surgical masks to commemorate Chow, and called for a moment of silence.

The university canceled classes and graduation ceremonies scheduled for the afternoon, while the student union called on students to participate in memorial services.

Meanwhile, protesters doubled down on their demand for an independent probe into the police force. The Civil Human Rights Front, organizer of massive street marches, called Friday’s development “the first death under the police actions” and warned that without a full investigation of the force, authorities risked pushing the city to “a situation where no one can recover.”

Hong Kong’s worst civil unrest in decades represents a political challenge to Chinese leader Xi Jinping, who is grappling with a slowing economy and a trade dispute with the United States. In Shanghai this week, Xi told Lam, Hong Kong’s embattled chief executive, that she still had the trust of the central government, following reports that Beijing was seeking to replace her.

Anna Kam and Tiffany Liang contributed to this report.