NAIROBI (AFP) -- A United Nations conference on electronic waste, so-called "e-waste", has opened with calls to protect developing nations from potentially deadly hand-me-downs from rich countries.

From used cellphones the size of a palm to computers to giant cargo ships, poor nations are at increasing risk from previously owned electronics and other items often, but not always, donated with good intentions, officials said Monday.

"One of the great challenges of our time is to collectively agree on what is waste and what are second-hand products," said Achim Steiner, head of the Nairobi-based UN Environment Program (UNEP) which is hosting the meeting.

"This question extends to end-of-life ships as much as to electronic goods," he said in an opening address, noting that marine vessels are increasingly fitted with sophisticated electronic components.

"Unless we get to grips with this, we are always going to be like the proverbial dog chasing its tail," Steiner said.

With many laptops, mobile phones and other electronic gadgets becoming obsolete within months of production, e-waste is the fastest growing part of municipal waste in the developed world, experts say.

Once discarded, or donated, much of it is shipped to developing countries, mainly in Africa, under the label of "refurbished goods", but they end up rotting in junkyards and releasing lead, cadmium, mercury and other deadly compounds.

Between 20 to 50 million tons of e-waste is generated in developing countries each year and while the exact amount reaching Africa is not clear, experts estimate that up to 75 percent of what arrives on the continent is useless and dangerous.

"We live in a world where new thinking is urgently needed," said Steiner, calling the safe disposal of e-waste "a real challenge" for the planet that will only get harder as technology continues to advance.

His comments came as delegates from the 120 signatory countries to the Basel Convention on the transport and disposal of hazardous waste, which took effect in 1992.

The week-long conference is expected to adopt a new framework on helping to protect developing nations from unregulated imports of e-waste, toxic chemical waste and other byproducts of development.

It is looking to develop schemes under which used end-of-life electronics products can either be taken back, recycled or accompanied by certificates proving they have indeed been refurbished and are functional.

Some delegates are urging countries like the United States, which is not a party to the convention, to join with the European Union that has for several years banned the export of hazardous electronic wastes.

The EU has also mandated the phase-out of toxic constituents in computers and required manufacturers selling electronic equipment in EU states to take back equipment at obsolescence to ensure its safe recycling.