Four prominent leaders of Hong Kong's democracy movement have been jailed for their role in organising mass protests in 2014 that paralysed the city for months and infuriated Beijing.

The prison terms are the latest hammer blow to the city's beleaguered democracy movement.

It has seen key figures jailed or banned from standing as legislators since their demonstrations shook the city but failed to win any concessions.

Nine activists were convicted earlier in April of at least one charge in a prosecution that deployed rarely used colonial-era public nuisance laws over their participation in the Umbrella Movement protests, which called for free elections to appoint the city's leader.

Their trial renewed alarm over shrinking freedoms under an assertive China, which has rejected demands by Hong Kongers for a greater say in how the financial hub is run.

Two key leaders of the mass protests - sociology professor Chan Kin-man, 60, and law professor Benny Tai, 54 - received the longest sentences of 16 months in jail, sparking tears in court and angry chants from hundreds of supporters gathered outside.

Two other leaders - activist Raphael Wong and politician Shiu Ka-chun - received eight months, while the rest either had their jail terms suspended or were given a community service order. 

One defendant, politician Tanya Chan, had her sentencing adjourned because she needs surgery for a brain tumour.

The jail terms are the steepest yet for anyone involved in the 79-day protest, which vividly illustrated the huge anger, particularly among Hong Kong's youth, over the city's leadership and direction.

As Wong was led away by guards he proclaimed: "Our determination to fight for democracy will not change."

Tai and Chan founded a civil disobedience campaign known as "Occupy Central" in 2013 alongside 75-year-old Baptist minister Chu Yiu-ming, one of the defendants to have his jail term suspended.

Their original idea of taking to the streets to demand a fairer system and the right to directly elect Hong Kong's leader was a precursor to the student-led Umbrella Movement a year later that brought parts of the city to a standstill.

Authorities in Hong Kong and the mainland have defended the prosecutions as a necessary measure to punish the leaders of a direct action movement that took over key intersections of the city for many weeks.

But activists and rights groups have argued that the use of the vaguely worded public nuisance laws, and wielding the steeper common law punishment, is an insidious blow to free speech and a new tactic from prosecutors.