Hong Kong has been plunged into the worst political crisis since its 1997 handover as pro-democracy activists take over the streets following China's refusal to grant citizens full universal suffrage.

Why is the city so divided?

Public discontent in the semi-autonomous city is at its highest in years. Rising inequality, competition for resources with mainlanders and the cost of living -- especially housing -- are partly to blame.

But the current crisis revolves around perceived political interference by Beijing and a debate over how the city's next leader will be chosen under planned reforms.

What are the differences?

The current chief executive, Leung Chun-ying, and his predecessors were elected by a pro-Beijing committee. China has promised to let all Hong Kong citizens elect their next leader in 2017. But only two or three candidates who have been vetted by a nominating committee will be allowed to stand.

Pro-democracy activists call the arrangement "fake democracy".

They believe a nominating committee would inevitably be stacked in Beijing's favour, disqualifying any candidate critical of the Communist Party.

Who are the pro-democracy activists?

A mixture of lawmakers, academics, students and ordinary citizens. The younger generation is generally more active in pro-democracy circles than their parents.

In an echo of the student-led democracy protests that hit mainland China in 1989, student groups in Hong Kong have been instrumental in sparking the current wave of protests.

Last week university students began a week-long class boycott and were joined by secondary school students on Friday outside the city's legislative assembly.

On Sunday Occupy Central with Love and Peace, a broad network of activists led by two academics and a pastor who had vowed for months to launch a civil disobedience campaign, threw their weight behind the students.

That spurred tens of thousands of supporters to hit the streets. Police trying to clear main roads responded with tear gas, pepper spray and baton charges.

Earlier this year Occupy organised an unofficial referendum in which almost 800,000 citizens voted overwhelmingly in favour of greater democratic freedoms than Beijing is granting.

Is everyone behind Occupy?

Far from it. In August a network of pro-Beijing groups organised an anti-Occupy protest march that drew tens of thousands -- although there were allegations that some protesters were paid or bussed in from the mainland.

But the scale nonetheless pointed to unease felt by some Hong Kongers -- particularly in the business community -- about the democracy camp's confrontational approach towards Beijing.

A number of businesses have taken out adverts in the local press saying the city's status as an international trading hub is at risk should Occupy go ahead with its takeover.

What will happen next?

Analysts say the likelihood of Beijing backing down is very slim. Much will depend on whether protesters can keep their momentum going and retain public support.

Hong Kong has not seen widespread political violence since the late 1960s and many protesters are woefully under-prepared for tear gas and pepper spray.

But the police use of such tactics appears to have hardened the crowds' resolve, with demonstrators refusing to heed government calls to withdraw.

After the violence of Sunday night, police appear to have adopted a softer approach, withdrawing riot police and trying to negotiate. It is unclear whether that will last if protesters continue to occupy the streets.

Meanwhile there is palpable fear that Beijing may decide to send in the People's Liberation Army, who maintain a garrison in the city.

Hong Kong's chief executive has rejected that idea, insisting the city can police itself.