A rail link would be the best way to connect Hong Kong's and Shenzhen's airports and boost ties between the two cities' aviation sectors, Chief Secretary Henry Tang Ying-yen said after a meeting with Shenzhen Mayor Xu Zongheng . Two joint taskforces will be set up soon - one to study inter-airport co-operation and the other to look at development of the Lok Ma Chau Loop. 'It seems railway would be the most efficient and convenient means of public transport between the two airports, which are 30km apart,' Mr Tang said. 'There is a lot of room for the two airports to complement each other's route network.' Joint research on building a sixth border checkpoint between the two cities - connecting Heung Yuen Wai in the northeastern New Territories with Liantang in Shenzhen - was nearly complete, Mr Tang said. 'It is expected the Hong Kong side will finish its study on land planning and road links for the checkpoint in the first quarter of next year,' he said. A group of Shenzhen officials led by Mr Xu started a three-day visit to Hong Kong yesterday. The two governments signed seven pacts to enhance co-operation in infrastructure development, environmental protection, urban planning, trade, tourism, technology and medical services. Environmental assessment would be a focus for the joint taskforce on how to develop the Lok Ma Chau Loop, a 1 sq km site beside the Shenzhen River, the chief secretary said. 'How to protect the eco-environment of the loop area poses a challenge,' Mr Tang said. 'The area has been deserted for a long time, but it might play a key role in the two cities' economic development.' The site came under Hong Kong's jurisdiction in 1997 when the river was straightened. Cleaning up the loop area would be costly, as it contains 4.5 million cubic metres of toxic mud. Mr Tang did not give a timetable for developing the loop area or building an inter-airport rail link. Both ideas were first floated in August by a think-tank as part of an ambitious proposal to make Hong Kong and Shenzhen a single metropolis and an economic powerhouse bigger than London, Paris, Chicago or Los Angeles by 2020. The Bauhinia Foundation Research Centre, which is close to Chief Executive Donald Tsang Yam-kuen, proposes that the Lok Ma Chau Loop become a 'special region within special regions', with simplified entry procedures for Shenzhen residents. The foundation says that if the metropolis maintained gross domestic product growth of 8 per cent a year until 2020, its GDP would reach US$1.11 trillion, putting it behind only Tokyo and New York. This month, the chairman of the Airport Authority, Victor Fung Kwok-king, said he expected closer 'formal' ties among the airports in the Pearl River Delta as the proximity of infrastructure meant they could not afford to compete.