Hong Kong restaurants have come up with a novel way to cut down on waste from food leftovers -- threatening to fine diners who don't eat up.

A number of restaurants in the Chinese city alert customers that they will charge them between five and 20 Hong Kong dollars (0.64-2.5 US dollars) if they leave any food on their plates, the South China Morning Post reported.

It said a handful of restaurants serving do-it-yourself hotpots, sushi and buffets had set up the system.

However, a restaurant industry group said the move was merely put in place to warn customers and that few eateries, if any, had actually fined anyone.

"The penalties listed on the menus are just for warning," Hong Kong Federation of Restaurants and Related Trades spokesman Simon Wong was quoted as saying. "Who can afford to lose customers?"

Hong Kong is facing a landfill crisis as space runs out for dumping the increasing amount of rubbish produced by the city's seven million people.

The government is reportedly looking into a scheme that will reprocess into compost some of the 700 tonnes of food thrown out each day by the city's huge hospitality industry.