HONG KONG (NYTimes) - Three masked explorers appeared atop an apartment tower in Hong Kong's North Point district and sent a black drone flying, over a clothesline, until it was buzzing more than 10 stories above the cars, trams and pedestrians on the street below.

If history was any guide, the explorers said, the building the drone was filming - a 1952 theatre with unusual roof supports - would eventually be demolished because it is not on Hong Kong's list of declared monuments.

The authorities are "renewing the city on behalf of the developers, not the people", said one of the explorers, who goes by the alias Ghost in videos and whose pollution mask and fingerless gloves gave him the air of a bank robber or graffiti artist.

The explorers belong to HK Urbex, a so-called urban exploration collective whose expeditions often require trespassing or walks through dark, abandoned or dangerous sites. But unlike some urban explorers, they do not court danger purely for its own sake. Their primary goal is to peel back layers of history - sometimes literally, by digging through dust and trash - and forge a video archive of Hong Kong's colonial-era environment.

"Until you peel them back, you don't know what existed before," said Ghost, 33. "Others are interested in the adrenaline rush, but we're interested in the story. What can it tell us about the past?" Many buildings that went up here before Hong Kong's 1997 return to China from British colonial rule have already been replaced by taller ones, as exceptionally high property values create economic incentives to cram more towers into an already crowded skyline.

But some buildings lie fallow for years between tenant evictions and demolition, and others, like the 1952 State Theatre that the explorers filmed recently, are partly open to the public. The State Theatre's main space, for example, is now a snooker hall. HK Urbex sees these structures as prime targets for urban expeditions.

So far HK Urbex has released more than three dozen videos documenting their perambulations through derelict prisons, tenements, cinemas, hospitals, casinos, police stations, bomb shelters, subway tunnels, a shipwreck and other sites across Hong Kong and elsewhere in Asia. Fans say the elegiac videos, cut with bleak soundscapes and often presented without narration, are poignant meditations on urban evolution and decay.

"It's about forcing us to confront the aesthetic of loss," Mr Lee Kah Wee, an assistant professor of architecture at the National University of Singapore, said of the group's film oeuvre. "It forces us to come face to face with this debris of modernization and these ruins that are constantly accumulating, even as we keep building."

The group says its most popular videos have been viewed more than 20,000 times on YouTube. Its photographs and videos have also been cited or featured in an international art exhibition, a forthcoming photography book and an advocacy campaign to save Central Market, a 1930s landmark in central Hong Kong, from demolition.

The group's eight members, all longtime Hong Kong residents, use aliases in their work to keep public attention focused on their mission instead of their personalities but also because anonymity helps shield them from potential legal trouble. They agreed to be interviewed on the condition that they be identified only by their aliases.

The HK Urbex members often spend weeks researching obscure and abandoned sites before visiting them. Once inside, they document everyday items that they stumble upon - family portraits, X-rays, ancestral shrines, a broken piggy bank - and that will probably never be recorded in history books.

"If not for this group of urban adventurers, all of these buildings would eventually disappear without anyone knowing what they meant to society at a certain point in time," said Mr Lee Ho Yin, the director of architectural conservation programs at the University of Hong Kong. He added that he regarded the group's members as "extreme urban anthropologists". The Hong Kong government's Antiquities and Monuments Office has granted 114 buildings and cultural landmarks permanent protection from development, and assigned grades to about 1,000 historic buildings, a list that may soon include the 1952 State Theatre.

But Mr Lee of the University of Hong Kong said that the second classification did not legally protect buildings from demolition, and that Hong Kong officials - unlike their counterparts in Singapore, another wealthy Asian city and former British colony - rarely bestowed conservation status on modernist landmarks like the State Theatre.

"Unfortunately, the economy of Hong Kong is still very much pegged to property development," he said.

A spokeswoman for the Antiquities and Monuments Office, reached by telephone, declined to comment on HK Urbex or its activities.

The group was formed in 2013 by Ghost and a friend, who goes by the alias Echo Delta. They both are part-time film-makers, and they discovered their initial HK Urbex sites while scouting locations for film shoots, Echo Delta said.

After a video they shot of a Hong Kong shipwreck received wide coverage in the city's Chinese-language news media, they said, they decided to create the HK Urbex Facebook page, and later a YouTube channel and Tumblr blog.

HK Urbex members say their videos are visual expressions of the "localist" political movement that has recently gained support in Hong Kong and reflects a conviction among many younger people that their city's identity is distinct from that of the Chinese mainland.

The localist movement is itself an outgrowth of the pro-democracy Occupy Central protests of 2014, which swept Hong Kong and reflected a widespread fear among many people here that Beijing is running roughshod over the "one country, two systems" principle governing Hong Kong's transfer to Chinese rule. The principle granted the city a high degree of legal, financial and political autonomy until 2047.

"I guess we're indirectly political," Ghost said, as Echo Delta's drone buzzed above North Point.

After filming the State Theatre, whose structural supports soar above its roof in concrete parabolas like those of a suspension bridge, Echo Delta and Ghost took a taxi to the city's Central district. The idea was to check on some abandoned buildings that they have been monitoring over the years.

One stop was Central Market, a 1930s landmark that Ghost had previously explored twice - first by sneaking past a security guard who was urinating and later by climbing in through a window.

This time, a side door was unlocked.

Echo Delta slipped inside, but a security guard quickly shooed him away.

"Sorry," he said.

On nearby Bridges Street, a white residential building that the pair had once sneaked into was now ringed by a fence, with "X" marks in its windows. "They've cleared it out," said Echo Delta, whose alias is a play on his real-life nickname.

Later, they saw that while several abandoned buildings near the Graham Street Market had been razed for new construction, others were still standing, right beside the market's open-air vegetable hawkers.

One squat apartment building in particular, which had plants growing in its crevices, caught their eye. They lingered for a few minutes under its shadow, apparently transfixed by its architectural features.

"Look at those long windows," Echo Delta said quietly. "Victorian - no, Georgian?"

"That would be one to look into," said Ghost, the only white member of HK Urbex. His alias plays on a Cantonese slang term for foreigners.

His partner nodded.

"I bet it's going to be turned into a Starbucks," Echo Delta said.