HONG KONG (REUTERS) - Discarded face masks are piling up on Hong Kong's beaches and nature trails, with environmental groups warning that the waste is posing a huge threat to marine life and wildlife habitats.

Most of Hong Kong's 7.4 million people have, for weeks, been putting on single-use face masks every day in the hope of warding off the coronavirus, which has infected 126 people in the city and killed three of them.

But huge numbers of the masks are not disposed of properly, and have instead ended up dumped in the countryside or the sea where marine life can mistake them for food. They are also washing up on beaches along with the usual plastic bags and other trash.

Environmental groups, already grappling with the flow of marine trash from mainland China and elsewhere, say the cast-off coronavirus masks have compounded the problem and also raised concern about the spread of germs.

"We only have had masks for the last six to eight weeks, in a massive volume... We are now seeing the effect on the environment," said Mr Gary Stokes, founder of the environmental group OceansAsia.

Mr Stokes cited the example of Hong Kong's isolated and uninhabited Soko islands, south of its international airport.

He said he initially found 70 discarded masks on 100m stretch of beach and when he came back a week later, there were more than 30 new ones.

"That was quite alarming for us," he said.

Other beaches around the city tell a similar story, he said.

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Densely populated Hong Kong has for years struggled to deal with plastic waste. A culture of eating out, fast food and takeaway has fuelled a rising tide of single-use plastic.

Very little rubbish is recycled, with about 70 per cent of the city's six million tonnes of waste a year ending up in landfill.

"Nobody wants to go to the forest and find masks littered everywhere or used masks on the beaches. It is unhygienic and dangerous," said Mr Laurence McCook, head of Oceans Conservation at the World Wildlife Fund in Hong Kong.

Conservation groups have been organising beach cleanups to tackle the trash.

The masks are made of polypropylene, a type of plastic, and are not going to break down quickly, said Ms Tracey Read, founder of the group Plastic Free Seas in Hong Kong.

"People think they're protecting themselves but it's not just about protecting yourselves, you need to protect everybody, and by not throwing away the mask properly, it's very selfish."