Reaction to the HK$65 billion cost of a planned cross-border high-speed rail line is not the government's only headache - officials are scratching their heads over how to set up a joint immigration checkpoint at its Hong Kong terminus without amending the Basic Law. The mini-constitution says that, with few exceptions, national laws cannot be enforced on Hong Kong soil, making it difficult to deploy mainland immigration officials at the West Kowloon station. Creative solutions being looked at include redrawing the border to put part of the terminus under mainland jurisdiction or confining mainland officials' powers to immigration clearance, without powers to search or arrest passengers. If a way is found for a 'one location, two inspections' system, the airport will be the next place on Hong Kong soil to get a joint checkpoint. A railway engineer involved in the project said the government's legal advisers were reluctant to give officials from the mainland the right to enforce its laws in Hong Kong, since that might involve an amendment of the Basic Law. 'Given the sensitive political atmosphere in Hong Kong, some may see it as the first step of a breakdown in the principle of 'one country, two systems',' the engineer said. For cross-border rail passengers to go through quarantine, immigration and customs clearance for both jurisdictions in Hong Kong, mainland officials would have to be allowed to exercise some of their laws in the city. But Hong Kong University law professor Eric Cheung Tat-ming does not see how this could be done. 'No other laws except our mini-constitution and the national laws specified [in it] are allowed to be practised on Hong Kong soil,' he said. 'I don't see how a different legal system can be enforced at a certain location in the city, unless that area is no longer considered part of Hong Kong.' The transport minister, Eva Cheng, said on Thursday that a joint checkpoint in West Kowloon involved complicated legal and security issues and she was not confident it could be established by the time the express line opens in 2015 or 2016. Even without a solution, a government official familiar with the project said, separate clearance was possible since the three mainland stops on the line to Shibi, Guangzhou, would have the necessary facilities. Alternatively, mainland immigration staff could perform inspections on the train. 'But none will give as much convenience as the joint checkpoint option, which allows commuters to transit to any mainland city after going through just one inspection.' The border-bending solution was practised in reverse to enable a joint checkpoint to be set up at the mainland end of the Western Corridor crossing over Deep Bay. Hong Kong's jurisdiction was extended across the mainland section of the bridge into the shared facility. 'The same could be done to Hong Kong, only in a reverse way,' the official said. The border could be extended through the tunnel connecting West Kowloon to the first stop at Futian, Shenzhen, to encroach on a small part of the terminus. The two checkpoints would be on the same floor of the West Kowloon terminus, divided by a line separating the two jurisdictions. The United States and Canada have for years stationed immigration staff from both countries on each other's soil to perform checks. Travellers who have passed US government checks in Canada, but whose plane or ship has not departed, remain under the legal jurisdiction of the host country. US officials may question and search travellers, but do not have powers of arrest, although they can stop them boarding their flight or ship. The Transport and Housing Bureau said the Department of Justice and Constitutional and Mainland Affairs Bureau were still negotiating with mainland authorities for a solution.