An official overseeing the pay-as-you-throw scheme said on Wednesday that it would not be ideal for building managers to buy large designated bags on behalf of all residents.

From April, people will have to dispose of household rubbish using designated bags, and it has been suggested property managers could buy 100-litre bags to place in communal bins used by residents.

Theresa Wu, an acting assistant director of the Environmental Protection Department, told an RTHK programme that such a practice would not be banned, but it is not encouraged.

"This will encourage or lead people to not abide by the law. And in the long run, you need to pay HK$11 every day, it's not cost-effective," she said, referring to the price of a 100-litre bag.

Peggy Lee, a Wan Chai district councillor, said many buildings are still discussing how to handle rubbish after the policy comes into effect.

"We discussed this at the district council meeting, and the Environmental Protection Department said owners' corporations may buy some designated bags for cleaners to deal with the garbage not thrown away in the bags," she told the same programme.

"But the corporations think it's not suitable to pay for those who violate the law to throw away their rubbish. If everyone does this, no one will use the designated bags."

Wu said they will investigate any complaints of serious illegal rubbish dumping, noting that they are launching a mobile app for people to file reports and upload photos of trash not put in a designated bag.

But Beatrice Siu from Greeners Action said only investigating complaints will not be good enough and the administration should also conduct random inspections.

She said building managers should take steps to deter violations of the policy.

"They have to be transparent about the number of bags they have used to deal with garbage thrown away in an illegal manner. I believe residents will then be alert, and may keep an eye on each other," she said.