A month into the mass pro-democracy protests gripping Hong Kong, the movement is under pressure to keep up momentum -- but those on the streets say their vigil has already changed the city for good.

On September 28, chaotic street battles in one of Asia's premier financial hubs saw umbrella-wielding demonstrators choking on clouds of police tear gas.

The ugly scenes triggered a wave of anger, with tens of thousands swelling the ranks of those demanding open leadership elections for the semi-autonomous Chinese city in 2017.

Four weeks on, protest camps remain sprawled across three major thoroughfares.

But the Chinese government shows no sign of backing down on its insistence that candidates for the city's top post be screened by a loyalist committee, a decision the protesters say is designed to ensure the election of a pro-Beijing stooge.

The crowds have thinned, and with Hong Kong's authorities apparently determined to let the protests lose steam as residents tire of the ongoing traffic mayhem, demonstrators are under increasing pressure to shift to tactics that would force a response.

But their leaders are unsure how to move forward. For Joshua Wong, the firebrand teenage activist and one of the most recognisable faces of the so-called "umbrella movement", the only certainty is that retreat is not an option.

"Occupiers are standing firm," he told AFP at the main protest camp outside government headquarters in Admiralty, central Hong Kong.

"Without any concrete result, all of the occupiers will sleep in their tents every single night."

Keen to reinvigorate the movement, organisers are planning a rally to mark the one-month anniversary of the protests later Tuesday, asking supporters to bring the same clothes they wore on September 28 -- including protective gear.

At 17.57 (0957 GMT) activists will hold an 87-second silence to mark the number of times police said they fired tear gas that evening.

- 'Utopia' in the heart of Hong Kong -

Those camped out in Admiralty express pride in their well-organised tent village, where litter is meticulously recycled, students complete their homework in a designated study area, and thousands gather at the weekends to cheer speeches from activists.

"This is Hong Kong's utopia," said 31-year-old protester Jimmy Leung as he strummed a guitar outside a friend's tent.

Surrounded by colourful protest art, many at the camps are delighted by the burst of creativity -- and a new sense of community -- in a city usually more preoccupied with making money.

"On this street, even if you don't know each other you can discuss issues around politics," said protester Wing Mak.

"It's not like before. Hong Kongers used to think of themselves as separate from society, without thinking about how we're intertwined."

But for Leung, life in "utopia" isn't quite perfect -- he's tired after 30 nights on what used to be a nine-lane highway, and desperate to see the protesters and government reach a deal.

"It's not that fun staying here," the freelance writer admitted. "But I think I should insist on what's right."

In talks with the protesters last week, Hong Kong's government offered tentative concessions, saying they would file a report to Beijing on recent events and suggesting that both sides set up a committee to discuss further political reform beyond 2017.

Neither idea met with much enthusiasm. And a street vote planned by rally organisers to decide how to respond to the government's offers was cancelled just hours before polling was set to begin on Sunday.

- Wider civil disobedience campaign? -

Some protesters grumble about the apparent lack of direction from their leadership.

"There's quite a lot of empty talk without solid proposals," said Wing Mak, 37, as she sat at the second-largest camp, in working-class Mongkok.

A wider programme of civil disobedience has been mooted -- with ideas ranging from refusing to pay tax to a slow-driving campaign -- while Benny Tai, co-founder of pro-democracy group Occupy Central, has suggested a Hong Kong-wide referendum on democratic reforms.

For the writer and veteran Hong Kong-watcher Nury Vittachi, regardless of how the standoff ends, the protests have breathed new life into a pro-democracy movement that has flagged since colonial power Britain handed the city back to China in 1997.

"Everybody knows now that what they're being offered is not real democracy -- it's 'choose your puppet'," he told AFP.

"The pro-democracy movement in Hong Kong was really moribund until a month ago. It had nearly died on its feet. Now it's back, with new faces."

While he does not expect Beijing to back down over the vetting of candidates, he believes the protesters could win some concessions, such as "tweaks" to the committee screening the candidates, or even the resignation of deeply unpopular Hong Kong leader Leung Chun-ying.