Davos (Switzerland) (AFP) - Forty of the world's biggest companies assembled in Davos agreed on Monday to come up with cleaner ways to make and consume plastic as waste threatens the global eco-system, especially in oceans.

The plan was announced at the World Economic Forum in the Swiss ski resort, where powerful executives are gathering just days ahead of the inauguration of Donald Trump as US president, who views concern about such environmental issues with suspicion.

The planet's dangerously polluted oceans will contain more plastic waste than fish by 2050 if urgent action isn't taken, the companies warned.

Answering a call by British sailor and philanthropist Ellen MacArthur, multinationals such as Unilever and Procter and Gamble made a commitment to increase recycling and cut back overall use.

Food-to-detergents giant Unilever said it would ensure that all of its plastic packaging "is fully reusable, recyclable or compostable by 2025".

The Davos initiative said 20 percent of the world's plastic production could be profitably re-used and a further 50 percent recycled instead of infesting landfills and killing wildlife in the ocean.

But even then, "without fundamental redesign and innovation, the remaining 30 percent of plastic packaging (by weight) will never be recycled and the equivalent of 10 billion garbage bags per year will be destined to landfill or incineration", the WEF said.

"The 'New Plastics Economy' initiative has attracted widespread support, and across the industry we are seeing strong initial momentum and alignment on the direction to take," said MacArthur, who is a regular Davos presence along with celebrities such as Matt Damon.

Other companies backing the initiative include Coca-Cola, Danone and Dow Chemical.

"Plastics are the workhorse material of the modern economy -– with unbeaten properties," said Martin Stuchtey, a professor for resource management at Innsbruck University in Austria who is working on the programme.

"Minor changes in material, format and treatment ... can make the economics of recycling viable and take us into a positive spiral of ... lower costs and better design," he said.