An official at Hainan's Transport Department confirmed feasibility studies would begin this year, adding that its Guangdong counterpart had started preliminary work on the project.

Feasibility studies and preliminary work for the 15.75 billion yuan project are expected to take five to 10 years.

Hainan Governor Wei Liucheng said the tunnel had been listed as an important project, and an expert committee had been set up to study it.

Supporters of the new link said it was needed because the existing Guangdong-Hainan rail-ferry link, which cost 4.8 million yuan to build, was a temporary solution to connect the island to the mainland.

The link, which has become a white elephant, consists of a 22.5km ferry service and 345km of railway track. Experts say it is limited in the volume of passengers and goods it can carry, and subject to the vagaries of weather.

A 2001 study by Wang Mengshu, of Beijing's Transportation University, found that the railway's capacity would reach its peak by 2017.

Linking Zhanjiang and Sanya, the railway is reportedly making only 60,000 yuan a day on cargo services, not enough to pay back the interest on loans to fund its construction. Plans to launch passenger services have been postponed indefinitely.

'The tunnel will be more convenient and time-saving than the railway,' said Chen Wen , the head of the Hainan studies department at the China (Hainan) Institute of Reform and Development. 'Once we have the tunnel, we won't be so cut off when there is a typhoon.'

The tunnel would be of more strategic significance in promoting growth than it would be economically viable, she said.

There was no immediate urgency to push for the undersea or bridge link because low demand did not justify construction in the near term, while the central government's focus was on completing the railway between Qinghai and Tibet .