Thousands of Hong Kong residents protested at the weekend over a government plan to build artificial islands to deal with the city’s severe housing shortage.

Hong Kong leader Carrie Lam last week announced a plan to reclaim about 1,700 hectares (4,200 acres) from the ocean and build infrastructure and transportation links to create a major business district. The islands, which would be Hong Kong’s largest land reclamation project, would eventually house up to 1.1 million residents over the next few decades.

Critics have said the project, the “Lantau Tomorrow Vision”, unnecessary, unaffordable, and unsustainable. Conservationists say it will destroy fisheries and marine habitats.

On Sunday, protesters took to the streets in central Hong Kong, carrying posters with the words: “We don’t want white elephant projects.” Children held up drawings of marine life and cutouts of Chinese white dolphins, whose population has already fallen dramatically over the years because of construction.

The Lantau project is the latest major infrastructure to come under fire from residents who say the government is wasting money on projects aimed at connecting the city more closely to mainland China. The Lantau plan is also being touted as another gateway to the Greater Bay area, a campaign to integrate Hong Kong with southern Chinese cities.

'This is part of the plan': new train blurs line between China and Hong Kong Read more

Proponents of the project say it is aimed squarely at one of Hong Kong’s biggest issues: a lack of affordable homes. Hong Kong, home to 7 million people, has some of the world’s most expensive housing. Lam promised 70% of the new land developed would be devoted to public housing.

The idea of using artificial lands for more housing has been debated on and off for years. Hong Kong’s airport is built on reclaimed land. About 6% of Hong Kong’s total area is built on reclaimed land, and about a quarter of the population is living on reclaimed land, according to a government taskforce.

Yet, sceptics say there is good reason why the Lantau project has not been acted upon yet. “Nothing has happened so far for two simple reasons: there is no real need for it, and the government does not have the money for it,” wrote Lam Chiu Ying adjunct professor in the geography and resource management department at the Chinese University of Hong Kong, for the South China Morning Post.

Pro-democracy parties say the project could cost as much as HK$1trn ($127bn), while other estimates put the cost at between HK$400bn and HK$500bn. The government has not released estimates but Hong Kong’s financial secretary admitted on Sunday it would be costly.

Others say the city still has existing land it could use – degraded agricultural land held by property developers, land reserved for indigenous villagers, or parts of the New Territories.

Critics also say the project will take too long to help with the imminent housing shortage. Construction would begin in 2025, with the first round of housing available only in 2032, according to the plan.

Pro-democracy lawmaker and environmentalist Eddie Chu said: “Hong Kong’s housing problem needs an urgent solution, like provisional housing, rather than a mega project that takes 20 years to finish.”