A band of Hong Kong art guardians are on constant standby at the city's sprawling protest site. Their mission: to swoop in and save a vast array of creative works -- including the towering "Umbrella Man" statue -- if the police move in.

Over nearly a month of protests calling for greater democracy in the southern Chinese city, a kilometre-long stretch of highway opposite the government headquarters usually choked with traffic has been transformed into a riotous open air exhibition.

At the centre sits what protesters have dubbed "Umbrella Man" -- a 12-foot tall wooden sculpture symbolising the protester's inventive use of umbrellas to defend themselves against everything from rain and tropical heat to police batons and pepper spray.

Walk through the camp and demonstrators can be seen sketching new works on the road in chalk or hand-crafting hundreds of origami umbrellas. Virtually every wall, central reservation and pillar has become a hanging space while large banners flutter from two bridges crossing the occupied thoroughfare.

All the while a team is on constant alert for any sign of an impending police crackdown.

"Their job is to call me," Meaghan McGurgan, who runs a theatre blog and founded the Umbrella Movement Art Preservation group, told AFP. "I can then mobilise the rescue teams standing by."

The political, grassroots nature of the protest works are far removed from Hong Kong's usual art scene, dominated by pieces that sell for record-breaking sums.

"Everyone can see it, everyone can go, everyone can participate," McGurgan said of the impromptu outdoor art venue.

But activists are acutely aware it could all be lost if the police attack.

- 'Museums scared of protest art' -

Much of the art at a secondary protest site in the working-class neighbourhood of Mongkok was destroyed in recent clashes with officers.

Numerous artists have already given their permission for volunteers to remove the pieces at the main site. But finding a place to store them has been more problematic, with the city's museums balking at taking the works.

"We phoned the museums," McGurgan said. "They either didn't get back to us, or said they wouldn't take the art as it was political. I thought that was really sad."

About a dozen galleries have stepped in to fill the void, offering to store the pieces safely until more permanent plans can be made. Trucks have also been donated and are ready to remove the pieces should police move in, she said.

For pieces such as "Umbrella Man" that task will hopefully be relatively simple: get in, grab the statue, and get out.

For the "Lennon Wall", however -- an emotive stretch of wall covered with thousands of sticky notes inscribed with messages from both supporters and detractors of the movement -- the task is more complex.

"We've taken large-scale photographs from far away and gridded them off into sections," McGurgan said of the fragile pink and yellow mosaic.

"If necessary we can put it all together again like a puzzle later on."

If the situation becomes too dangerous to remove the art safely, she added, UMAP's volunteers will do their best to document "the destruction of something beautiful".

That material would then be added to a digital archive that UMAP is also building, potentially even using it to recreate any pieces that might be destroyed.

- The spaces between -

It's not just the art that activists are struggling to preserve.

The Umbrella Movement Visual Archive and Research Collective, another organisation coordinating with UMAP, is working with volunteers to document "how people form a community here, and how they transform the space", said one of its founders Sampson Wong.

That includes everything from street signs that have been altered to show pro-democracy slogans or poke fun at politicians, to the living spaces that protesters are creating at the site.

"Basically you have all parts of life in place here in a different way," Wong said.

The group aims to launch a website archiving the material and an interactive map of the site using crowd-sourced images and stories, Wong said.

Like UMAP, Wong's group has people standing by should chaos break out to retrieve the smaller, more ordinary things that help make up the site.

"But obviously once the objects are taken away from here they are decontextualised, they are leaving their context, so we very much don't want to do that until the last moment," he said.

Local artist Kacey Wong says the democracy movement's protest art needs to be preserved for future generations.

"I don't know what is the future of Hong Kong but right now it looks grim," he said.

"If that is the case, then the children 25 years from now should be able to look back on a world that was highly civilised and full of hope."