Xu said these so-called fifth-freedom rights will feature in the next round of Hong Kong-mainland air services negotiations expected to take place this year.

Currently, Hong Kong-based carriers can offer point-to-point passenger and cargo services between Hong Kong and 45 mainland cities, but once they have landed in China, they are not allowed to go on to another international destination.

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Albert Yau, general manager for cargo at Hong Kong Dragon Airlines, said fifth-freedom rights could conflict with the Basic Law, Hong Kong's mini- constitution, which enshrines the principle of "one country, two systems."

If the mainland were to allow Hong Kong carriers to pick up passengers or cargo in Shanghai for transport to the United States, for example, the US government would have to talk with both the Hong Kong and central governments; otherwise it would violate the one-county, two-systems principle, he said. Yau added fifth-freedom rights might also damage Hong Kong economically, since passengers and cargo would no longer need to stop in Hong Kong before going on to the mainland. However, Hong Kong's former director of civil aviation, Peter Lok, said the Basic Law is not in danger of being violated.

According to Basic Law Article 132, he said, all agreements providing for air services between Hong Kong and other states and regions involving stops in the mainland must be concluded by the central government.