Environmentalists lashed out Thursday at a proposal by the Hong Kong government to create 25 man-made islands off the city's coast, claiming effects on marine ecology would be "irreversible".

In a desperate attempt to ease land shortage, officials proposed the creation of a 1500-hectare man-made giant island and 24 other smaller islands on Wednesday.

If constructed, the mega artificial island would have an area larger than the island reclaimed for Hong Kong's international airport and would require claiming land from sea up to 14.5 metres deep, the government said.

But environmentalists are concerned that the proposed sites will affect the Southern Chinese city's natural shorelines.

"The impacts brought by reclamation projects are irreversible and particularly damaging, and it should be avoided in and around areas of high ecological and fisheries importance," Samantha Lee, senior conservation marine officer of World Wildlife Fund Hong Kong told AFP Thursday.

In particular, the landfill will affect areas of "extremely high ecological importance", she said, including the habitats for the Hong Kong endemic Bogadek's burrowing lizard and 30 species of soft corals, gorgonians and black corals.

"WWF urges that the government think thoroughly about such far-reaching plans," Lee added.

Government officials would not confirm that sites chosen for reclamation were only intended for housing and said they could become sites for facilities such as oil depots or factories, which would free up land in the urban area for other developments.

Last year, Hong Kong leader Donald Tsang pledged to tackle the city's soaring property prices and vowed to further boost the city's land supply in response to rising public anger over soaring property prices.

Demand from wealthy Chinese investors has driven apartment prices beyond the reach of many low and middle-income earners in the Asian financial hub of around seven million people.