With a surface area 50 percent bigger than Singapore, the island has captured the imagination of developers, who have considered building everything from a Disney theme park to a replica of Michael Jackson's Neverland ranch.

Some fear a parade of eager investors buoyed by the new transport links could ruin the rustic island and its vast wetlands, but officials insist the site will not become a stomping ground for land grabs and overdevelopment.

"We believe the negative impact from the bridge will be almost negligible," Zhao Qi, the Shanghai government official in charge of Chongming, told reporters during a visit ahead of Saturday's opening to normal traffic.

Two more bridges are planned that will connect Chongming to eastern Jiangsu province as part of a national highway to central Xi'an, and to Shanghai's Pudong International Airport, city construction commissioner Huang Rong said.

Chongming earned global attention in 2005 when then-British Prime Minister Tony Blair and Chinese President Hu Jintao said it would be the site of the world's first so-called "eco-city" Dongtan, designed by a British firm.

The low-carbon, ultra-efficient city of the future was meant to be showcased at next year's World Expo in Shanghai, with 25,000 residents living there, but those plans have been overtaken by more traditional development objectives.

Zhao insisted the Dongtan plan had not been shelved for good, saying only it was "still in the planning stages".

Officials promote Chongming as the "last virgin island" and the "Shangri-La of Shanghai" but it is hardly unspoiled wilderness.

More than 700,000 people live there, and the population is projected to rise to two million within the next decade.

Residents currently depend on 18 ferry routes to reach the mainland, so the new bridge clearly will allow for faster commuting -- and will spell big bucks for investors.

But many are concerned that the island could fall prey to unscrupulous developers.

Philip Enquist, a Chicago-based architect with Skidmore, Owings and Merrill, was hired by the Shanghai government to design a master plan for the island, which included compact communities spaced about 16 kilometres (10 miles) apart.

But he has heard nothing from officials for two years, when the Shanghai planning board handed authority over Chongming to a different department, and he fears the bridge will bring unchecked construction.

"Chongming runs a huge risk of being poorly developed because it's now accessible to Shanghai. There are very little constraints and there's a lot of open land there," Enquist told AFP.

Chongming's wetlands, which are home to several species of rare migratory bird, its proximity to Shanghai and its position at the mouth of the Yangtze combine to make the island a rare gem that should not be sullied, he said.

"It could play a very unique role and it shouldn't be built into the same suburban-ness that so much of Shanghai is turning into," said Enquist, who also designed the master plan for the development of Abu Dhabi.

Zhao insisted the government had embraced a broader definition of the island's "ecology" to ensure that development did not come at the price of the environment.

"We will stress the environment has a limit of what it can handle. Based on what the environment can handle, we will make proper investments to upgrade people's living standards and boost economic development," he said.

(c) 2009 AFP