Executive councillor Bernard Chan has waded into the controversy over where to find land to build more homes.
He urged a debate on alternative options to boost supply, not just by cutting into country parks but by including other land such as farmland.
He was shocked to learn that less than 7 per cent of Hong Kong's total land area was zoned residential and said an informed discussion was needed.
Chan is the first Exco member to respond to a blog post on Sunday by development minister Paul Chan Mo-po that the city could consider using sections of country parks for housing.
Chief Executive Leung Chun-ying said the government had made no decision on use of the parks, but remained firm that flat-sale duties introduced to cool the housing market would stay.
"When the city's population is jammed into 6.9 per cent of the land, the living conditions are going to be bad," Chan told the Post. "Society should conduct an informed discussion about what we want. You can't have everything."
But he said the public should not focus only on country parks, which comprise about 40 per cent of the city's area. "Country parks included, [the green belt] comprises more than 60 per cent of the area. Other land uses, such as farmland, can be discussed."
Chan said he loved the parks. "Of course I want to keep them. But it is something society has to debate. [Can we discuss ] reclamation, or farmland, or industrial zones for residential use?"
Housing Society chairman Marco Wu Moon-hoi said the ratio of country park land was negotiable.
"Must we always only contemplate the idea of expanding country parks, but can never cut into the country park land?"
Leung said the question of whether flats could be built in country parks had been floated from time to time and the government "has no decision so far".
He also insisted the government would not back down on its doubling in February of the stamp duty on flat purchases.
"Any form of change, such as exemptions or a tax rebate, would reduce the impact of the doubling of stamp duty, affecting the stability of the financial system and the property market," he said.
Leung was responding to calls for exemptions for charities and religious groups and Hongkongers buying flats via companies.
He said: "After consideration we found it is not easy for [any exemption] not to be exploited."