The environmental lobby group said it had found five sites in the southern Chinese enclave's rural north where large stockpiles of discarded computer monitors, keyboards, circuit boards and components had been stored.

The parts had leached harmful lead, which Greenpeace said was present in concentrations 5-10 times the normal level.

"This heavy metal is highly toxic to plants, animals and humans," the organisation said in a statement.

Greenpeace said the e-trash was mostly imported from overseas and was being stored in Hong Kong to get around mainland China's laws forbidding direct trade in such harmful materials.

"The huge volume of cross-border trade between Hong Kong and China attracts traders in e-waste from developed countries to use Hong Kong as a stopover," it said.

"The e-waste is then imported into China by road, making inspection more difficult."

The organisation called on Hong Kong's government to tighten controls on the import of e-waste and urged it to support calls for gadget manufacturers to make greater efforts to ensure better disposal of their discarded products.

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