During an investigation from July to August, the green group found illegal activities on at least 35 brownfield sites. In many of these sites, rubbish hills comprising of metal waste, circuit boards, plastic wraps and construction waste were found to have piled up, covering a total of 10 hectares.

The worst was at Ha Tsuen in Yuen Long, where nine rubbish hills spanning 7.7 hectares were found. Each hill is about five to eight meters high.

Greenpeace found that the soil from the hill contained zinc and copper at levels that are in excess of Dutch standards on heavy metal pollution.

The group suspected that the metal waste was imported from overseas and processed in Hong Kong before being resold overseas.

The site in Ha Tsuen was estimated to contain metal waste weighing 51,000 tons.

The Planning Department said that the Town Planning Board never gave approval for the development in Ha Tsuen. The department will follow up on illegal establishments and carry out prosecution if there is enough evidence.

The Lands Department said operators in Ha Tsuen are ordered to leave by the end of this month. Follow up action will be taken if there is illegal occupation of government land.