China will expand its ban on imports of solid waste, local media reported on Monday, almost a year after its first curbs caused havoc in countries that sent their rubbish to the Asian giant.

The regulatory action — which expands the prohibition to 32 categories of solid waste from the 24 banned last year — will go into effect from December 31, according to official news agency Xinhua, citing four Chinese government agencies.

Newly banned product types include hardware, ships, auto parts, stainless steel waste and scrap, titanium and wood, Xinhua said.

The initial ban caused worldwide problems as recyclers were cut off from their main market for waste material.

Globally, since 1992, 72 per cent of plastic waste has ended up in China and Hong Kong, according to a study in the journal Science Advances.

China bought up more than half of the scrap materials exported by the US last year, but that proportion has been falling with Beijing's regulatory moves cutting down the types of waste Chinese companies could buy.

China says the policy changes are in line with a new push to protect the environment. They suggest Beijing no longer wants to be the world's trash can, or even its recycle bin.

Equally damaging for recyclers have been more stringent policies on the quality of waste China will allow across its border.

For products such as cardboard and metal, China set a contamination level of 0.5 per cent last year; an extremely low threshold that required US and other recyclers to change technology and sorting techniques to meet the new standards.

Global plastic exports to China were forecast to fall from 7.4 million tonnes in 2016 to 1.5 million tonnes in 2018, while paper exports might tumble nearly a quarter, according to one researcher.