A green group said on Thursday that while its study has found a significant drop in the number of plastic bags being given out at supermarkets after the levy was doubled to HK$1, over-packaging is still a major cause for concern.

Greeners Action conducted the field study from mid-January to early this month at 54 supermarkets across the territory, and found an almost 90 percent drop in the number of flat-top plastic bags distributed at cashiers, compared to a previous study conducted in June last year.

"Under the new legislation, we found that many supermarkets have taken away flat-top bags from the vegetable section, so the customers cannot get it easily by themselves," said the group's executive director Angus Ho.

Under the new levy scheme that came into effect on December 31, stores can no longer hand out free bags for food items wholly wrapped in non-airtight packaging, such as bags of apples.

In a separate study conducted this month, the group also found that more than three quarters of the 206 vegetable samples it looked at were wrapped in plastic. In one case, three layers of plastic were used to wrap a grapefruit.

"Over-packaging has been a problem for a long time already. But after the implementation of this new legislation, some products are even more packaged, in order to avoid the confusion of customers... whether it can be [exempted] or they still have to pay," Ho said.

The NGO called on supermarkets to avoid overpackaging, and urged the government to introduce relevant laws to address the problem.