Reports that a garrison of Chinese border guards has taken over land on Hong Kong's side of the internal border, which its personnel also cross at will, have sparked protests in the former British colony over promises that the city would remain a separate jurisdiction after the 1997 handover.
The investigative journalism group FactWire found that some 21,000 square feet of privately owned land within a high-security area along the Hong Kong side of the border with mainland China has been used by the 6th Detachment of the Guangdong provincial border defense corps of the People's Liberation Army (PLA) for the past six years.
It said the border guards had also built themselves a small bridge over the Sha Tau Kok river, which runs along the border at this point, and "frequently" use it to enter Hong Kong incognito.
Lawmakers from the pro-democracy Civic Party gathered on Tuesday outside government headquarters, shouting "One country, two systems! Don't allow our border to be breached!"
Lawmaker Alvin Yeung said the group is demanding an explanation from the city's government over the reported encroachment onto Hong Kong's territory, which was supposed to remain a separate immigration territory under the terms of the 1997 handover to China.
"They should explain to the people of Hong Kong whether or not the territory in question belongs to Hong Kong, and, if it does, why the PLA has been coming and going freely [over the border] without any supervision," Yeung said.
Democratic Party lawmaker James To said he was very disappointed in the government's failure to make any information public on the matter so far.
"It's pretty scary that the PLA has occupied a piece of land and is coming to and fro freely ... we don't know if there are illegal goings on within the army itself such as smuggling, or other things that haven't yet come to light," To said.
"Maybe it's money-smuggling -- that's something even President Xi Jinping would be anxious about," he said, in an apparent reference to the president's anti-corruption campaign and ongoing bid to prevent corrupt officials from getting huge sums of money out of the country.
Illicit vegetable patch
The illicit vegetable patch lies around one kilometer from the Sha Tau Kok border crossing on the Hong Kong side, squarely in the territory of the Hong Kong Special Administrative Region (SAR), which maintains its own border controls.
A nearby sign says that the land was turned into a "green garden" in 2012 by border guards "with the support of superior authorities" to rear fish and poultry and grow vegetables.
The river -- a narrow creek at this point -- was diverted to the south of the vegetable patch at around the same time, FactWire said, but no changes were made to the border, which still runs to the north of the area.
Meanwhile, the border garrison in Shenzhen has private and unchecked access to a large tract of woodland on the Hong Kong side the border.
"The Hong Kong-Shenzhen border runs through the middle of the bridge, but FactWire has witnessed at least five soldiers, dressed in camouflage fatigues, crossing the invisible border and moving gunny bags and wheelie bins back and forth across the bridge," the agency said.
It cited Google satellite images of the area as showing that the river had run along the border back in 2010, but was bent southwards into Hong Kong in 2012, around the time when the border guards started growing food on the land.
Hong Kong chief executive Carrie Lam on Tuesday said her government was "concerned" at recent media reports.
"We are concerned after hearing some of these media reports, and the relevant departments are in the process of investigating the matter," Lam said. "We will make the results of our investigations public when they are available."
"There are no updates to share with you for the time being," she added.
Fears about Hong Kong's special status
Parts of the border area near the Shenzhen River were developed between 1995 and 2006 by the Hong Kong and Shenzhen governments, which saw the relocation of border fencing as well as redrawing of parts of the border, but the border garrison's vegetable garden wasn't part of that project, the report said.
However, FactWire quoted the garrison's commanding officer as saying that anything north of the Sha Tau Kok river was also north of the border.
He said his personnel were allowed to access the closed border area without permission from the Hong Kong side "to arrest smugglers or illegal immigrants," it said.
The report came amid growing concerns that Hong Kong's promised special status is fast eroding, in the wake of a series of cross-border detentions by Chinese police and the targeting of anyone involved in public discussion of separatist ideas.
Just three weeks after the opening of a huge sea-bridge linking Hong Kong to mainland China, local residents have protested loudly over a sudden surge in visitor numbers, saying they are unable to find anywhere to eat or sit down at peak times of day.
Residents on Hong Kong's Lantau Island have complained about serious overcrowding at weekends since the bridge opened, with concerns being raised that many visitors are on unlicensed tours organized by mainland travel agencies.
Some 96,500 people passed through the bridge's Hong Kong port last Sunday, slightly down on the 102,900 seen the Sunday before, government broadcaster RTHK reported.
Reported by Lau Siu-fung for RFA's Cantonese Service, and by Jia Ao and Hwang Chun-mei for the Mandarin Service. Translated and edited by Luisetta Mudie.