HONG KONG (Reuters) - Hong Kong announced on Tuesday a controversial plan to allow mainland officials to enforce Chinese laws inside a Hong Kong train station, an immigration set-up critics say will encroach on the city’s autonomy and endanger existing freedoms.

Hong Kong’s Basic Law mini-constitution states that with a few exceptions Chinese national laws are not applicable in the city and no Chinese departments can interfere in its affairs.

But the local government said Mainland Port Areas inside the train station, set to open in autumn next year, will be legally regarded as being outside the territorial boundary of Hong Kong, so that articles of the Basic Law do not apply.

A former British colony, Hong Kong returned to Chinese rule in 1997 and enjoys wide-ranging freedoms not granted in mainland China and an independent judiciary under a so-called “one country, two systems” formula.

But the abduction by mainland agents of Hong Kong booksellers in 2015 who had published critical books on China, and Beijing’s efforts to disqualify democratically elected opposition lawmakers in the local legislature, have rattled confidence in that arrangement.

About a quarter of the planned train station for high-speed trains linking Hong Kong to the mainland will fall under mainland Chinese jurisdiction, the government said.

These areas include two immigration halls at the West Kowloon station where Chinese officials will clear passengers’ departure to and arrival from China, platform areas and even inside the train before it leaves Hong Kong.

“STARTLING”

Hong Kong’s legal chief, Rimsky Yuen, denied the government was effectively ceding land, saying the local government had proposed the idea to maximize the railway’s potential.

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“The implementation of co-location arrangement is neither a directive nor an order by the Central People’s Government,” Yuen said, adding that it would need the consent of both governments.

The case would not set a precedent, he added, but stopped short of ruling out similar future arrangements.

The move is a “stark” and “startling” change to the “one country, two systems” model, said Simon Young, a law professor at the University of Hong Kong.

“It’s a remarkable exception ... just carving out space in the heart of Hong Kong and placing it under mainland jurisdiction, even the train carriages,” he said.

“It suddenly opens all kinds of legal questions and possibilities and I would urge the government to clarify these in detail.”

Chief Executive Carrie Lam’s top advisory body, the Executive Council, approved the plan on Tuesday.

The government is expected to formally reach a pact with Beijing and seek endorsement from China’s top parliamentary body, with a bill later going to the city’s legislature.

The railway, embroiled in controversy for more than seven years, could serve as a new rallying cry, particularly with memories of the disappearing booksellers still fresh.

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But the city’s opposition has lost most of its veto power in the 70-member legislature after Hong Kong courts expelled six pro-democracy lawmakers.

At a cost of more than HK$84 billion ($11 billion), the Express Rail Link will roughly halve the journey between Hong Kong and the southern Chinese city of Guangzhou to 48 minutes.

It will save passengers about 39 million hours of travel time each year, it said on its website, equivalent to HK$90 billion in economic benefits in 50 years.

Hong Kong now has direct train services to Beijing, Shanghai and several cities in southern Guangdong province. Passengers go through immigration on arrival at Chinese terminals.

Since 2007, a similar arrangement has operated at the border where Hong Kong jurisdiction overlaps with areas of the Shenzhen Bay Port on the mainland.

The government has yet to hammer out all the details of the arrangement.

Asked if passengers could access Facebook, which is blocked in China, while they wait for trains in the Hong Kong station, Yuen said he did not know.

“I think it’s a very good question. I would like to find out the answer later myself.”

($1=7.8085 Hong Kong dollars)