Zhu Wenhui, a consultant at the Bauhinia Foundation Research Centre's Hong Kong-Shenzhen Metropolis Study Group, said should the proposed metropolis keep an 8 percent gross domestic product growth per annum, its GDP would reach US$1.11 trillion (HK$8.66 trillion) by 2020.

That would make the metropolis the third-largest economy, after Tokyo and New York, in the world, surpassing major cities like London, Paris and Los Angeles. If a 6 percent projection is adopted, the megacity would still rank fourth in the world.

The foundation proposed 10 recommendations to achieve that status, one of which involves the building of a high- speed railway connecting the airports of the two cities forming a super air hub.

"With the direct express link, the journey time between the Shenzhen Bao'an Airport and Hong Kong's Chek Lap Kok International Airport will just be 17 minutes, with trains presumably running at 140 kilometers an hour," Zhu said. But he admitted the financial and technical feasibility of the rail link is for the two governments to analyze. Hung Wing-tat, a Polytechnic University associate professor from the civil and structural engineering department, said the proposed railway would not be feasible, given it covers major existing navigation routes.

In a statement, a spokeswoman from the Transport and Housing Bureau said there exists great room for cooperation between the two airports.

"We already plan to suggest building the Tuen Mun western bypass and another link of Tuen Mun and Chek Lap Kok ... to shorten the journey between the two airports," she added.

An Airport Authority spokeswoman said it will keep an open mind to any proposal that is beneficial to strengthening the airport as an international or regional hub.

Another proposal involves the issuing of electronic multiple-entry visas in the first stage and which would enable two million permanent Shenzhen residents more convenient access to Hong Kong.

"Such visas would greatly reduce the time needed for customs clearance from the existing 45 minutes to as little as 15 minutes," Zhu said, adding with easier access, 88 percent of Shenzhen residents surveyed had indicated they would travel more frequently to Hong Kong.

That, together with enhanced transport networks, would allow the metropolis to become what Zhu termed a "one- hour metropolitan life cycle."

A spokesman for the Security Bureau said the suggestions were noted and the views of various parties would be fully considered in the light of actual circumstances.

Other recommendations include the establishment of a "Hetao Development Management Authority" to actively promote development of the Hetao area near Lok Ma Chau and enabling more Shenzhen students easier access to study in tertiary education institutions in Hong Kong.

Foundation chief Anthony Wu Ting-yuk said the report was compiled after thorough research over the past eight months and involved interviews with 100 government officials and experts from both sides of the border, 150 enterprises in the two cities and 1,000 Shenzhen citizens.

The highest-ranked local official consulted, the foundation said, was at the permanent secretary level.

On a national level, opinions of officials from the Commerce Ministry, National Development and Reform Commission and the State Council's Hong Kong and Macau Affairs Office were also collected.

Zhu said the report gained the support from 90 and 60 percent of Shenzhen and Hong Kong officials, respectively.

"The 30 percent of [Hong Kong] officials with reservations were mostly concerned with technical issues arising from the integration," Wu said.

He admitted the concept is a very complicated issue that involves the cooperation of not just the governments in Hong Kong and Shenzhen, but also the central and Guangdong provincial governments.

"As a think-tank, we hope more discussion can be brought about on an important issue to the development of the region and the nation ... and hopefully governments can use the report as a starting point for a [policy] breakthrough," he said.

While admitting competition exists between the two cities, Wu said "an enlarged pie" would constitute a win- win situation amid healthy competition.

Lawrence Lee Kam-hung, the convener of the study group, stressed the research report was compiled without the blessing of the central government.

In response to the report, a Constitutional and Mainland Affairs Bureau spokesman said the government has all along attached importance to the cooperation between Hong Kong and Shenzhen.