New designated bags for household rubbish went on sale on Friday, even though their use won't be mandatory until August.

The bags, priced at between HK$0.30 and HK$11 depending on the size, are available in a range of shops.

A shopper in Lok Fu surnamed Pun told RTHK he would be making good use of the special bags to take his groceries home in, noting that the smaller ones are cheaper than the HK$1 bags shops provide at check-outs.

"I will buy designated plastic bags, because I can use them to dispose of trash at home later. So, if I do not have my shopping bag with me, I would prefer to buy designated plastic bags," he said.

Another shopper, a woman surnamed Chan, said the arrival of the green bags was news to her and she wouldn't be buying any just yet.

"I have a lot of white plastic bags which I bought earlier. I will use them up first and buy the designated ones on August 1st," she said.

Secretary for Environment and Ecology Tse Chin-wan urged people to only buy genuine designated bags from stores that display a tag from the Environmental Protection Department.

He said buying counterfeit bags won't be illegal – but from August 1, using them to throw out rubbish will be.

"The government departments are very concerned about anybody selling unauthorised bags or even fake bags. Therefore, they will work together to conduct surveillance in the market as well as over the web. Whenever they find such cases, they will certainly take actions under the law," Tse told reporters.