China, however, is pushing back on the targets, according to a diplomatic note issued by Beijing.

Shipping, which transports around 90% of world trade and accounts for nearly 3% of the world's carbon dioxide emissions, is facing calls from environmentalists and investors to deliver more concrete action, including a carbon levy.

"I urge you to leave London having agreed a greenhouse gas strategy that commits the sector to net zero emissions by 2050 at the latest," Guterres said in a recorded address.

"And that includes ambitious science-based targets starting in 2030 – both on absolute emissions reductions and the use of clean fuels."

Guterres said such targets would provide "the certainty that the industry and investors need".

Member countries of the U.N.'s shipping agency, the International Maritime Organization (IMO), are meeting in London this week. They will adopt an upgraded greenhouse gas emissions strategy whose specific details are being discussed.

In addition, there are also proposals for a levy on global carbon dioxide emissions on shipping.

The IMO has so far pledged to halve greenhouse gas emissions from ships by 2050, from 2008 levels - a commitment that lags EU and U.S. plans to reach zero net emissions by that date.

According to a note seen by Reuters that was issued by China and circulated to developing countries, Beijing said, "developed countries are pushing the IMO to reach unrealistic visions and levels of ambition, especially requiring the international shipping industry to reach life cycle zero GHG emissions by 2050 at the latest".

The note added that China objected to using "revenues for purposes of general climate changes adaptations out of the shipping sector".

When asked to confirm the note, which was first reported by the Financial Times, China’s foreign ministry spokesman Wang Wenbin told reporters in Beijing on Monday that China believed the IMO should "take into account different national conditions" and "accommodate the legitimate concerns of developing countries".