Enforcing a law against smoking near the windows and in the balconies of homes cannot be compared with a probe into the offence of a person being naked at home while exposed to public view, said Minister for Sustainability and the Environment Grace Fu on Monday.

"One can smell smoke even without having sight of the smoker, nor the ability to pinpoint where the smoke is coming from," she explained in a written response to a parliamentary question filed by Mr Louis Ng (Nee Soon GRC).

"But to impose a fine on the smoker, we need evidence to show the act of smoking, not merely the smell of the smoke."

Given the current technology, it would be challenging to track down the smoker or obtain evidence of an act of smoking being committed without rather intrusive methods, Ms Fu said, adding that this would affect even the privacy of innocent neighbours.

"And such efforts may still be futile if the smoker hides behind a pillar, frosted glass windows or curtains to avoid detection," she said.

In contrast, a complainant would be able to more easily pinpoint the location and capture evidence of a nude person exposing himself or herself to public view, to assist with investigation, she added.

Mr Ng first called for a ban on smoking near the windows or in the balconies of homes early last October.

He said then that while such a move might seem intrusive, there were already laws in place to police people's behaviour at home - such as Section 27A of the Miscellaneous Offences (Public Order and Nuisance) Act, where one cannot bare it all, even in private, while exposed to public view.

In a Facebook post at the end of October, Mr Ng wrote: "Being naked in your own home doesn't kill your neighbour but second-hand smoke could."

But Ms Fu said the frequency and nature of going in the buff and going for a puff were different and the two matters should not be compared directly.

Still, she assured Mr Ng that tackling second-hand smoke was a priority for her ministry, which is focused on encouraging individuals to be more socially responsible and facilitating conversations between neighbours.

Ms Fu also noted that smoking is prohibited in more than 32,000 locations here, including covered common areas right up to the doorstep of homes. This includes hawker centres, in view of a long-term plan to transition them into completely smoke-free spaces, she said in a separate written response to Ms Tin Pei Ling (MacPherson).

Since 2015, the Ministry of Sustainability and the Environment has required newly built and renovated hawker centres to be smoke-free. Ms Fu said that as at last month, the number of hawker centres with smoking corners had been whittled down to 27 out of 114.

The National Environment Agency will engage the likes of hawkers' associations to progressively remove the remaining smoking corners when there are opportunities such as during repair works.

Ms Fu also noted that as of last October, hawker centres undergoing the Toilet Improvement Programme (TIP) could get up to 90 per cent funding if they remove smoking corners.

"I urge town councils to apply for the TIP to upgrade the hawker centre toilets and rescind smoking corners at the same time," she said.