Brazil and South Africa have joined calls for a new global climate pact, leaving China, the United States and India still to come on board, Europe said Friday as the UN talks went down to the wire.

The two emerging giants rallied to a proposal supported by the European Union, least-developed countries and vulnerable small-island states, said European Climate Commissioner Connie Hedegaard.

"Brazil (is) also in favour, South Africa OK for a legally binding deal," she told journalists in Durban.

"That is half of BASIC, now we are waiting for the other half," she added, referring to India and China, the first and third largest carbon polluters in the world.

They, along with the number two emitter the United States, have not endorsed the European proposal for a mandate for a new accord embracing all major carbon emitters.

"Although there are these encouraging signs, we are definitely not there yet and time in Durban is now really short," Hedegaard said, adding that closed-door discussions would now pick up after breaking off at 4:00 a.m. (0200 GMT).

Earlier Friday, the EU said it had formed an alliance with some 85 of the world's most vulnerable nations to push for the new global pact on greenhouse gases.

"The least developed countries, the Alliance of Small Island States (AOSIS) and the European Union are united in their desire for an ambitious outcome in Durban," the three blocs said in a joint statement.

"We believe that the world has had a lot of time to think. What we need is not more thinking. What we need is more action."

But Hedegaard cautioned that the gap in positions remained wide and did not rule out a breakdown.

"If there is no further movement from 4:00 am then I don't think there will be deal in Durban. That is what we are faced with," she said.

The EU is calling for a new round of pledges under the Kyoto Protocol, and a "robust mandate and roadmap for a legally binding instrument."

Going into the talks, Kyoto -- the only international curb on greenhouse gases -- was hanging by a thread.

Key countries had announced their refusal to renew carbon-cutting pledges at the end of next year when the treaty's first round of cuts expires.

The EU said it would renew its vows, but only if major emitters -- including the US and China -- would commit to forging a new climate deal by 2015.

For AOSIS nations and many poor African states already suffering climate impacts, that was not soon enough.

"The gap between our ambitions and the current pledges is simply too wide," the joint statement said.

"The facts are clear and we are still too far from where we need to be to secure the most vulnerable countries' right to sustainable development."

It did not not specify a date for a new pact, though.

Current voluntary pledges running to 2020 to reduce CO2 emissions fall far short of what is needed to prevent the planet from heating up by more than 2.0 degrees Celsius (3.6 degrees Fahrenheit) beyond pre-industrial levels, scientists say.