Hong Kong's pro-democracy occupation is entering its death throes with radical splinter groups pushing for more direct action but others urging retreat, analysts said Tuesday.

But regardless of how the occupation ends, the protests have already had a lasting impact on the city's political landscape, mobilising unprecedented numbers and fostering political debate, they said.

The largely peaceful movement saw tens of thousands take to the streets at its height, but violent clashes between police and protesters Sunday highlighted frustrations as students have failed to win concessions on political reform.

Teenage protest hero Joshua Wong and two other student leaders have embarked on a hunger strike. But the original founders of the civil disobedience movement took a step back Tuesday, saying that they would "surrender" to police and urging students to climb down.

The Beijing-backed government has stood firm against the protesters and as they scramble to find an effective counter-strategy, analysts say that the fragmented occupation movement has entered a decisive phase.

"It is going towards the final showdown. When and how remains to be seen," said political expert Sonny Lo of the Hong Kong Institute of Education.

"Some will give in sooner or later, some will stay on and some will resist police action. There will be a real risk of more violent confrontations by the more radical wing."

Student-led demonstrators are demanding free leadership elections for the semi-autonomous Chinese city. Their main protest camp blocks a long stretch of a multi-lane highway in the Admiralty district of central Hong Kong.

Moderate pro-democracy legislators as well as the "Occupy Central" founders -- two academics and a Baptist minister -- have long been leaning on the students to back away from confrontation, and now the public is also growing tired of a movement that has brought parts of the city to a standstill.

"It looks like we are seeing the tail end of this particular phase of the movement," said political analyst Willy Lam of the Chinese University of Hong Kong.

"(Occupy Central founder) Benny Tai and the pan-democratic lawmakers have been putting pressure on them all along to have a voluntary strategic retreat... and public opinion has turned further against continuation of the occupation."

With one major protest site already cleared and an injunction now in place to clear parts of the main Admiralty site, the authorities have suggested further police action is imminent.

- 'Pressure to escalate -

But with student leaders anxious not to walk away empty-handed, there are those who will refuse to go away quietly.

Sunday saw hundreds pushing through police lines towards the government complex in Admiralty, and in November windows of the legislature were smashed as some protesters tried to break in.

"The movement organisers are under pressure to escalate. But they are well aware that they can't win by more confrontations and they have a hard time to think of a reason to retreat without gaining anything. It's a dilemma," said Hong Kong-based political analyst Ma Ngok.

Lam added that while Joshua Wong's hunger strike is a move away from more aggressive tactics, the movement may swing into action again if the fast is ineffective.

"When the hunger strike is finished, more students might tend towards radicalism... they will be telling everybody 'we have tried everything, we have tried patient negotiation and then the hunger strike, so what's left except for escalation of action?'"

China's communist authorities insist that candidates for the 2017 vote must be vetted by a loyalist committee, which the protesters say will ensure the election of a pro-Beijing stooge.

But talks between demonstrators and the Hong Kong government in October ended in an impasse, with protest leaders saying authorities had little to offer.

Three student leaders were also denied permission to board a flight to Beijing last month where they hoped to bring their demands for free elections to Chinese authorities.

The government and Beijing's intransigence may now trigger a trend towards more radical protest even after the current occupation ends, said Ma, in a city in which peaceful mass protest marches have long been a regular occurrence.

"There is a possibility that future protests will be more confrontational and radical because people believe the more conventional forms of demonstrations -- rallies and petitions -- will not have any effect as the government will not listen to you," said Ma.

But the occupation has also had a positive lasting effect on the level of political awareness and debate in the city, says Lo.

"It has had a tremendous impact on society -- an unprecedented number of citizens have been mobilised by this debate over the Occupy movement to think about Hong Kong's politics -- in terms of the educative function, it has achieved what core leaders announced (as their intention) last year -- to educate the public, to mobilise the public."