“Despite it being a good thing to improve the tight living conditions in Hong Kong, it is worth discussing whether we still need the reclamation project,” Yip said. “The population growth will definitely be slower than the government estimate … The city may not be able to digest the supply.”

But a bureau spokesman earlier defended the need for the two mega projects, arguing society had reached a consensus on speeding up land supply for housing and economic development.

“The city needs the Northern Metropolis and the artificial islands,” he said. “Society has reached a consensus on speeding up quality land supply for housing, social and economic development. I think residents have such expectations.”

The three artificial islands under the Lantau Tomorrow Vision project call for building 210,000 flats for half a million people and a new business hub on an initial 1,000 hectares (2,471 acres) of reclaimed land in two decades. But the project, announced in 2018, assumed the population would rise to 8 million within two decades.

According to a government projection made in 2020, the number of residents will peak at 8.108 million in 2041 before gradually falling. But the population has dropped for two consecutive years, going from 7.481 million to 7.291 million, amid a declining birth rate and increase in migration. Many residents who have left the city pointed to strict Covid-19 pandemic rules and changes to the political landscape.

Price tag for artificial islands off Hong Kong’s Lantau balloons to HK$580 billion

Yip also noted the timeline for the reclamation project overlapped the one for the Northern Metropolis, which aims to build up to 926,000 flats to house 2.5 million people in the New Territories near the mainland border.

Chan Kim-ching, founder of the NGO Liber Research Community which focuses on land policy research, questioned whether the city still needed to create more land by mega reclamation projects. He instead urged accelerating development of the city’s brownfield sites, or damaged agricultural lands mostly occupied by warehouses.

Chan also warned that the price tag for the reclamation, which had already shot up by 16 per cent from the HK$500 billion predicted in 2019, would rise to more than HK$800 billion due to inflation and expected higher construction costs.

“The reclamation will take place in waters with an average depth of eight metres,” he said. “The islands have to be built taller to combat possible flooding. With these technical factors and higher construction costs, the current reclamation cost will double.”

Greenpeace Hong Kong senior campaigner Chan Hall-sion also argued the government’s estimate had overlooked inflation over the coming decades. If costs increased annually by an average of 3.59 per cent, as they had over the past four years, the price tag could reach HK$643 billion, she warned. Adding the cost of other parts of infrastructure in the mega project, the final bill could reach HK$799 billion, she said.

Hong Kong public’s views to be considered in plans for reclaimed land off Lantau Island

Under a design unveiled by the Development Bureau on Tuesday, the three islands will be linked by a mass transit system. But a proposed route for a railway going to the New Territories will now continue north to Hung Shui Kiu to connect with a suggested line to Qianhai in Shenzhen, instead of running along the south of Tuen Mun as previously suggested. A new 13km road will also connect the new area with Hong Kong Island and Lantau Island.

When the previous administration unveiled the project, it estimated the islands would generate HK$925 billion in land sale revenue. But according to the government’s latest estimates, about HK$750 billion is expected from auctioning off sites to developers, a drop by nearly a fifth.

Lau Chun-kong, a veteran surveyor and member of the government’s advisory panel that studied the reclamation proposal, defended the need to ramp up Hong Kong’s long-term land reserves.

“We have a policy to compete for talent, improve our competitiveness and attract more companies, as well as to maintain our position as an international financial centre. To do all these, we will need to increase our floor area,” Lau said.

Lam Chiu Ying, a former director of the Hong Kong Observatory, said the project would cost more as the government would have to build longer sea walls to combat flooding.

He noted the mainland had stringent rules on reclamation in place since 2018, adding: “The city is not contributing to the country’s biodiversity and ecological value when the city is still calling itself a metropolis.”