Rich and developing countries broadly agree over the scale of the crisis that threatens the ecosystems and species that humans rely on for food, climate regulation and economic prosperity.

But they are at loggerheads over how to go about how to pay for nature conservation.

The talks are overshadowed by geopolitical tensions, with countries facing a range of challenges from trade and debt worries to Russia's invasion of Ukraine.

While Washington has not signed up to the UN's Convention on Biological Diversity, new US President Donald Trump has moved to halt development funding through the United States Agency for International Development.

After two days of talks, negotiators were presented late Wednesday with a new text seeking to navigate between hard-fought red lines on whether to set up a specific biodiversity fund.

"We have no time to waste and the world is watching us, and we have a collective responsibility to show the world that multilateralism can work," said Steven Guilbeault, Canada's Environment minister.

Scientists have warned that a million species are threatened with extinction, while unsustainable farming and consumption ares destroying forests, depleting soils and spreading plastic pollution to even the most remote areas of the planet.

In a landmark 2022 agreement, countries agreed to halt the destruction of nature by the end of this decade.

Countries have already agreed to deliver $200 billion a year in finance for nature by 2030, including $30 billion a year from wealthier countries to poorer ones.

Debate now mainly centres on the way in which funding is delivered.

- 'Disappointed' -

Developing nations -- led by Brazil and the African group -- want the creation of a dedicated biodiversity fund, saying they are not adequately represented in existing mechanisms.

Wealthy nations -- led by the European Union, Japan and Canada -- say setting up multiple funds fragments aid.

Disagreement over this saw the previous UN COP16 talks in Cali, Colombia in November stretch hours into extra time and end without a deal.

Negotiators have until the end of the day on Thursday to hammer out a plan, with a proposal on the table to push back the ultimate decision on a new fund to future UN talks, while suggesting reforming existing financing.

Brazil, which is hosting UN climate talks later this year, warned that the painful progress on finance could reverberate across other treaty negotiations this year.

"We are definitely a bit disappointed," said Brazil's negotiator Maria Angelica Ikeda, speaking on behalf of the BRICS country bloc that includes Russia, China and India, in the Wednesday evening plenary.

"We will need to have more assurances that we won't feel abandoned in the future."

The failure to finalise agreement in Cali was the first in a string of disappointing outcomes for the planet at UN summits last year.

A climate finance deal at COP29 in Azerbaijan in November was slammed as disappointing, while separate negotiations about desertification and plastic pollution stalled in December.