Ministers acknowledged they had to start making giant strides before the arrival of 120 heads of state for the summit's climax on Friday.
Sources said the developing countries walked out of working groups at the start of the second week of negotiations, angered that in their view the conference was weakening in support for the Kyoto Protocol, the core emissions-curbing treaty.
The move was unleashed by African countries, with the support of the G77 group of developing countries.
They refused to continue negotiations unless talks on a second commitment period to the Kyoto Protocol were given priority over broader discussions on a 'long-term vision' for co-operative action on climate change.
The Kyoto Protocol ties the rich countries, but not developing countries, that have ratified it to binding emissions curbs.
It does not include the US, which says the Protocol is unfair as the binding targets do not apply to developing giants that are already huge emitters of greenhouse gases.
A first round of pledges under Kyoto expires at the end of 2012, and poorer nations are seeking a seven-year commitment period.
The walkout delivered another blow to the summit which has already been marred by spats between China and the US.
In an apparent concession, China said it might not take a share of any Western funding for emerging nations to fight climate change.
However, in a pointer to the tensions backstage, Vice Foreign Minister He Yafei said China would not be the fall guy if there were a fiasco.
The UN's climate pointman Yvo de Boer said the talks had made ground in the first week and insisted progress would become smoother.
Campaigners were even blunter, with Greenpeace saying the summit had five days 'to avert climate chaos' and emissions targets so far offered by Western leaders such as US President Barack Obama amounted to 'peanuts'.
The gathering's daunting goal is to tame greenhouse gases -- the invisible by-product derived mainly from the burning of coal, oil and gas that traps the Sun's heat and warms the atmosphere.
Scientists say that without dramatic action within the next decade, Earth will be on course for warming that will inflict drought, flood, storms and rising sea levels, translating into hunger and misery for many millions.
The stakes were underlined when a new UN report said that some 58 million people have been affected by 245 natural calamities so far this year, more than 90% of them weather events amplified by climate change.
And a study from the International Union for the Conservation of Nature, an intergovernmental group, said climate change threatens the survival of dozens of animal species from the emperor penguin to Australian koalas.
