"Resist colonial [rule]," he shouted. "Self-determination for Hongkongers."

Alex Chow Yong-Kang, the federation's secretary general, laid out the demands: let the public nominate candidates, abolish bloc-voting by interest groups in the legislative council and reject Beijing's elections plan.

"Class boycotts may last for only a week, but there could be more strikes in the future," Chow told the crowd.

"Who can say it's impossible to change this society?"

Watch: Thousands of Hong Kong university students join week-long class boycott for democracy in late September

Over the next five days, the student protest morphed into a massive sit-in that has gone on for two weeks.

Protesters, furious they were unable to reach Civic Square, pushed past police and poured onto Connaught Road Central, overtaking cars and buses. Within hours, they would establish a protest camp around the government offices and on the highway. Ignoring calls by officials to stop, protesters commandeered metal gates, barricading key city arteries, and turned Admiralty and Central into self-sufficient barracks with food, water, masks and goggles trucked in by allies.

Their efforts - blasted by city officials as illegal - sparked sister sit-ins in Causeway Bay and Mong Kok in Kowloon, the latter sparking violence. Chief Executive Leung Chun-ying dispatched an emissary to start talks with the students, only to pull out when protesters vowed not to back down.

"Students and people who support democracy have begun a new era of civil disobedience," Benny Tai Yiu-ting, co-founder of Occupy Central, told a crowd early on September 28.

The next day came Leung's defeated rejoinder: "It will last for a relatively long time."

Occupy Central with Love and Peace - to give that part of the protest movement its full name - had vowed to stage a massive sit-in in Central, shutting down the business district, if the government did not guarantee full suffrage in 2017. Some in the group seemed near to tears on August 31 after the National People's Congress Standing Committee laid out its election rules.

Watch: A recap of Hong Kong's Umbrella Movement in 5 minutes

On September 26, about 200 young people broke through the fences of government headquarters in Admiralty. Police with riot gear drenched them with pepper spray. Officers arrested more than 70 protesters, including 17-year-old activist Joshua Wong Chi-fung.

A significant section of city residents were incredulous - how could police hold a teenager for for protesting?

Furious, thousands arrived at government centre that Saturday night. The pressure was on Occupy Central organisers to start the sit-in. Just before 2am on September 28, Benny Tai declared that the civil disobedience campaign had begun.

Later that day, police barred protesters from returning to the site. At the barriers on Harcourt Road, hundreds of people - prepped for pepper spray with goggles and inverted umbrellas - pushed against officers in riot gear. Crowds pouring out of Admiralty station pushed and broke through a cordon. They climbed onto Connaught Road Central, stopping cars and buses.

"It wasn't what I expected but it felt good," musician Victor Au Chung-wing, 23, remembered thinking.

Then a police superintendent commanding the area gave a new order. Shortly before 6pm, with tens of thousands of people lining the highway, ramps, lower roads and sidewalks, police shot round after round of tear gas canisters. Screams rose from the smoke. Au said each breath felt like hot exhaust rushing to his lungs.

"Shame!" the crowd screamed, as some threw water bottles at the officers.

The crowds grew that evening with fathers, mothers and middle-aged residents furious with the violence they had seen on television. Later, the officer in charge of the operation defended the use of tear gas, saying the alternative - a baton charge - would have hurt people much more.

Rumours swirled - of tanks and rubber bullets, that Beijing would deploy the PLA.

Protester Kenneth Wong, 25, stood before some 10 police officers at the car park entrance next to Civic Square. "I want to tell them they are Hongkongers as well, and they also have a choice," he said. "I'm standing here, without any mask, to tell them they are doing something wrong. I have no fear."

Before midnight, Occupy Central co-organiser Dr Chan Kin-man said the protesters should retreat. Police hit another group with tear gas soon after - the last of 87 rounds fired that night and early the next day. Authorities said 46 people were injured.

Leung asked for calm. "I'm now asking them to fulfil the promise they made to society and stop this campaign immediately," he said on September 29. Instead, the next day, the students federation issued an ultimatum: Leung must step down by October 2 or demonstrators would storm government buildings, including Leung's office.

Many Hongkongers supported the students. The Professional Teachers Union called on teachers to strike. Secondary pupils boycotted classes. Some workers walked off their jobs. Many people said they were driven by the hostile police tactics, not the political agenda.

Demonstrators massed in Causeway Bay and Mong Kok. Student leaders called on shops to close and for students to indefinitely boycott classes.

On October 1, the Federation of Students offered to talk with Chief Secretary Carrie Lam Cheng Yuet-ngor, as long as Leung resigned first. He refused.

Leaders at the University of Hong Kong and Chinese University asked strikers in Admiralty to evacuate. The students held their ground. Leung appointed Lam to meet student leaders, opening a door to dialogue. But he said he would not resign.

On October 3, in Mong Kok, anti-Occupy Central demonstrators broke through police lines and started wrecking protesters' tents and attacking students. The crowd swelled to the hundreds with fights breaking out every few minutes. Anti-Occupy protester Jackson Tsui, 46, said he came to tell the crowds to go home. "They are seriously affecting the lives of ordinary Hong Kong people," he said.

A young man complained that police - who were clearly outnumbered - did not intervene when he was attacked by masked men. "People kept beating me after I fell", he said, a cut on his head bleeding.

Nineteen people were arrested, eight with ties to triad gangs. Several women said they had been groped. Secretary for Security Lai Tung-kwok later denied accusations that the police colluded with criminals.

The next day, the federation agreed to return to negotiate with officials on condition that the government investigate claims that police aided the thugs. Three rounds of preliminary meetings seemed to spark more rows.

As the week dragged on, the crowds at Admiralty, Causeway Bay and Mong Kok thinned. Sometimes just a couple of students sat outside the chief executive's Office. More people pleaded with students to disperse, including Catholic Cardinal Joseph Zen Ze-kiun.

The students had made their point, even some sympathisers argued. They were only harming their relations with the public.

As students called for more protests, and pro-democrats vowed to stall government actions, Carrie Lam called off talks planned for Friday. The students issued a new call: Hongkongers should occupy "every inch of the streets". We still don't know when - or how - it will end.