A number of representatives left the large main hall, with one representative shouting loudly when asked about the status of a deal: "Rejected!"
"We are here to negotiate but we have left the room because at the moment we don't have the feeling that we are being heard," Colombia's Environment Minister Susana Muhamad told reporters.
European delegation sources at COP29 said they assumed that the negotiations, which had been due to end on Friday before being extended, would continue.
Various draft texts are circulating among negotiators in Baku.
The European Union, United States and other wealthy countries at the summit agreed to raise their offer of climate funding to $US300 billion ($A462 billion) per year by 2035 to help developing countries grapple with climate change, sources told Reuters on Saturday, after a previous proposal was dismissed as insultingly low.
The summit had been due to finish on Friday but ran into overtime as negotiators from nearly 200 countries - who must adopt the deal by consensus - tried to reach agreement on a climate funding plan for the next decade.
Wealthy countries have offered $US300 billion a year of climate funding for developing countries. (AP PHOTO)
A $US250 billion proposal for a deal, drafted by Azerbaijan's COP29 presidency on Friday, was deemed woefully insufficient by developing countries.
Several groups of countries are demanding more ambitious commitments by industrialised countries to aid funding for action on climate change and adaptation in the coming years.
But a rough draft of a new proposal to curb and adapt to climate change on Saturday was getting soundly rejected, especially by African countries and small island states, according to messages relayed from inside.
The "current deal is unacceptable for us. We need to speak to other developing countries and decide what to do," Evans Njewa, the chair of the Least Developed Countries group, said.
With tensions high, climate activists heckled US climate envoy John Podesta as he left the meeting room.
They accused the US of not paying its fair share and having "a legacy of burning up the planet".
The last official draft on Friday pledged $US250 billion annually by 2035, more than double the previous goal of $US100 billion set 15 years ago but far short of the annual $US1 trillion-plus that experts say is needed.
Developing countries accused the rich of trying to get their way - and a small financial aid package - via a war of attrition.
And small island countries, particularly vulnerable to climate change's effects, accused the host country presidency of ignoring them for the entire two weeks.
After bidding one of his suitcase-lugging delegation colleagues goodbye and watching the contingent of about 20 enter the meeting room for the EU, Panama chief negotiator Juan Carlos Monterrey Gomez had enough.
"Every minute that passes we are going to just keep getting weaker and weaker and weaker. They don't have that issue. They have massive delegations," Gomez said.
"This is what they always do. They break us at the last minute. You know, they push it and push it and push it until our negotiators leave. Until we're tired, until we're delusional from not eating, from not sleeping."
With developing countries' ministers and delegation chiefs having to catch flights home, desperation sets in, Power Shift Africa's Mohamed Adow said.
"The risk is if developing countries don't hold the line, they will likely be forced to compromise and accept a goal that doesn't add up to get the job done," he said.
with DPA and Reuters
