Lawmakers and concern groups on Tuesday gave mixed reactions to the updated plan to build artificial islands off Lantau.

The estimated cost for the massive reclamation project has risen to HK$580 billion, HK$80 billion more than initial forecasts in 2018.

In a paper submitted to the legislature, the government said the plan now is to build three islands with a Y-shaped water channel running between them. They will be kept away from the surrounding natural islands by water channels, according to the paper, to avoid impact on coral of ecological value.

DAB lawmaker Edward Lau backed the plan, saying the authorities need more land at their disposal.

He said even though the project could be more expensive, the bill would still be similar to costs for land resumption in other areas, and the transport infrastructure that comes with the scheme would improve Hong Kong's overall transport network.

Originally, the project included a rail link connecting Hong Kong Island with the Kau Yi Chau Artificial Islands, north Lantau and Tuen Mun.

However, the end point in the New Territories has now been changed to Hung Shui Kiu, for what officials called a strategic connection with the planned Hong Kong-Shenzhen Western Railway.

Because of this, Roundtable lawmaker Michael Tien said he would "oppose until the bitter end" the rail route change, saying it disregards the transport needs of people living in the Tuen Mun area.

"[The authorities] are switching that alignment to Hung Shui Kiu coming straight down, and neglecting the transport needs of 500,000 Tuen Mun residents," he told RTHK.

But Tien said the project is a good one in general, saying land sales should still be able to cover the project's cost despite a fall in home prices.

The Liber Research Community, meanwhile, expressed concerns that the eventual cost of the project would go a lot higher than the estimated HK$580 billion because of inflation and more complicated reclamation works.

"The water depth [for the works] right now is almost 1.5 times deeper [than the original plan]. This difference in depth may cause some uncertainties in engineering works," said Caesar Choi, a researcher with the the land think tank.

He reiterated that his group thinks that reclaiming man-made islands is not necessary, as it estimates that there are 2,000 hectares of brownfield land in the New Territories that could be used for housing.

The Our Hong Kong Foundation said it thinks the updated estimate of the cost of the project is reasonable, saying long-term development plans shouldn't be changed because of short-term economic fluctuations.

A Development Bureau spokesman said further studies are needed to ascertain exactly how much the project will cost. But he said price shouldn't be the only factor in play as the project will help supply more housing, more quickly.

Asked why the rail link route has changed, he said Hung Shui Kiu is at the mid-point of the western New Territories, which would benefit residents of both Tuen Mun and Yuen Long.

The spokesperson added that authorities will conduct a two to three month public consultation early next year, to seek advice from District Councils and professional bodies, and plan to apply for funding for the reclamation works in the second half of 2025.