There will also be exclusive entrances and car parks for the chief executive, ministers, executive councillors and other prominent visitors to the new headquarters.

Lawmakers from the pro-democracy camp and a human rights group have criticised the tunnel as a way to allow the chief executive and his cabinet members to avoid protesters and the media. But a government spokesman stressed the passageway was aimed only at connecting the buildings.

At present, the chief executive and his cabinet members have to pass a protest zone before entering the Central Government Offices and Legco.

'Are they really so afraid of the Sun?' asked Law Yuk-kai, director of Hong Kong's Human Rights Monitor. 'This underground link will enable officials to hide. If the government does not facilitate protests, people will only turn to more radical acts.'

Under the design detailed in the prequalification document for tenders, the new headquarters, including the Chief Executive's Office block and the main government office building, will be placed under tight security control. Access by staff, visitors, as well as delivery and maintenance contractors to the buildings, will be separated and regulated.

The Chief Executive's Office building will not be connected to any other block except at ground level.

The main government office tower will have no direct connection with public transport or other private buildings without access control. In case of emergency, a system will be able to isolate the entire government headquarters.

The document does not specify or reserve any zone for demonstrations.

Democratic Party chairman Lee Wing-tat said the tight security would bar the public from the government headquarters.

'This underground tunnel means people can't hand their petition letters to the chief executive and ministers when they attend the Legco or Exco meetings. This is very bad,' he said.

Civic Party lawmaker Alan Leong Kah-kit said the design would make the chief executive, 'detached from the people ... These security measures are too tight and totally unnecessary. This fails to bring the government closer to the public'.

But a spokeswoman for the Administration Wing said the underground passageway was needed to link the government buildings and that the other security arrangements were put in place for the smooth and safe operation of the government.

According to the plan, the structure of the government headquarters will be resistant to fire, explosion and natural disasters such as earthquakes. Its building service system will be able to ensure quick recovery from sabotage and natural disasters.

'The design will have adequate robustness to avoid situations where damage to small areas of a structure or failure of single elements may lead to the collapse of the building,' the document reads.