Supporters of the planned co-location scheme in Hong Kong often point to US-Canada border preclearance procedures as a justification for joint checkpoint arrangements. The two systems, however, are very different.
Under the co-location scheme, the Hong Kong government may lease some of its land, namely sections of the railway station in Kowloon together with the platforms and rail tracks all the way to the Mainland border. This leased portion of land would basically fall under Chinese jurisdiction, and Mainland laws would apply and be enforced by Chinese officers.

In the US-Canada case, US border agents in selected airports work on Canadian soil and only have the power to enforce American immigration rules. They can screen, search and refuse entry to travelers before they board, but US laws do not apply in these preclearance areas. Since preclearance areas are still on Canadian soil, crimes committed in these areas would be handled and investigated by Canadian officers, and suspects would be tried in Canada in accordance with Canadian laws. In other words, travelers clear US customs and immigration whilst still on Canadian soil, but they don’t actually enter the US until they physically cross the border.
Like all systems, preclearance is not perfect. For one, crimes committed after departure could still result in jurisdictional conflicts in the context of cross-border law enforcement. In addition, there have been concerns about new powers recently granted to US border agents working on Canadian soil, such as the right to carry firearms and to temporarily detain and question prospective travelers.
While these changes were controversial in Canada, they came nowhere close to the planned co-location arrangement in terms of their legal and political implications.

Supporters of the co-location scheme are right to praise the convenience of joint checkpoint arrangements, but convenience cannot be an answer to legal and political concerns. Sure, joint checkpoints are convenient. But why is it that, in Hong Kong, the establishment of such checkpoints necessarily has to result in parts of Hong Kong’s territory becoming under Chinese jurisdiction? The adjournment of yet another bill committee meeting earlier this week due to failure to reach the quorum testifies of the enduring controversiality of the project.
If the end goal really is convenience, and if US-Canada preclearance can be used to justify joint checkpoints in Hong Kong, wouldn’t it be worth emulating the arrangement? That is, could a system be designed so as to grant Mainland border agents the right to be stationed in Hong Kong alongside local law-enforcement personnel to allow (or deny) travelers entry into China?
Although Article 18 of the Basic Law mentions that “National laws shall not be applied in the Hong Kong Special Administrative Region”, border agents would not enforce laws, but apply immigration rules by pre-authorizing entry into China. Such arrangements would also comply with Article 22 stating that personnel from central government departments can work in Hong Kong, and that they should abide by local laws.
There would be legal and constitutional hurdles to overcome in designing such a system. However, government officials and pro-establishment lawmakers have shown no lack of creativity in circumventing such hurdles with their co-location project. A preclearance scheme shouldn’t constitute an insurmountable challenge to their ingenuity. In fact, there would probably be a stronger constitutional basis for preclearance than for the proposed co-location arrangement.

Many people in Hong Kong have raised concerns about the government’s use of legal means and arguments to achieve political objectives, or simply for the sake of administrative expediency. A willingness to consider alternative arrangements could go some way in alleviating such concerns.
At the very least, supporters of the co-location plan should refrain from using US-Canada preclearance arrangements as a justification for their agenda. This is disingenuous. The two systems are completely different.