Two harbour protection lobby groups have called on the Trade Development Council to stop the planned $1.3 billion expansion of the atrium at the convention and exhibition centre.
The groups - Designing Hong Kong Harbour District and Citizen Envisioning @ Harbour - said the expansion would severely damage the Wan Chai waterfront.
Meanwhile, members of the government's advisory Harbourfront Enhancement Committee have reportedly expressed concerns about the expansion - saying it may pre-empt public consultation on the Wan Chai and Causeway Bay waterfront.
Paul Zimmerman, convenor of Designing Hong Kong Harbour District, said: 'The waterfront will never be the same: the sea view the public enjoys will be gone forever. It is against the integrated harbour-planning principle.'
The proposed extension of the annex highlighted the lack of co-ordination in the government on developments affecting the waterfront, he said.
The Executive Council's approval of the plan was announced on Thursday.