The climate change talks in Durban were in trouble on Friday night as China's chief negotiator firmly rejected proposals for a new global treaty on greenhouse gas emissions.

Su Wei said the proposals were unacceptable because they would lead to the end of the Kyoto protocol, the world's only existing treaty stipulating emissions cuts. He told the Guardian: "The G77 [group of more than 100 developing countries] could not take this [proposal] as the basis for discussion. This is killing the Kyoto protocol. They want to finish the Kyoto protocol."

Seyni Nato, spokesman for the Africa group at the talks, said: "We are not happy with the [negotiating] text." He said he too feared the proposals as tabled would mean the end of the Kyoto protocol. However, he acknowledged: "This is only a first draft. We are in for a very long night."

Their words were at odds with the upbeat assessment given by European negotiators, who said the "tempo" of the negotiations had picked up and were moving in the direction of an agreement. They said it was untrue that the G77 had rejected the proposals, and that most developing countries were still in support.

Governments from 194 nations were wrangling into the early hours of the morning over what form any future agreement on global warming should take, and whether poor countries should carry legal obligations to cut their emissions, as well as the rich.

At stake was also the future of the Kyoto protocol, the only legal treaty forcing rich countries to cut their greenhouse gas emissions. If the talks collapse, the protocol will be in effect dead after its current provisions expire at the end of next year.

EU member states, with a handful of allies including Norway and Switzerland, are the only developed countries prepared to carry on with the Kyoto protocol. The US has always rejected the 1997 pact, and Japan, Canada and Russia have declared they will not take on new emissions targets under the protocol beyond 2012.

But the EU will only agree to a "second commitment period" covering emissions from 2012, probably until 2020, if other countries sign up to a "roadmap" for a new global agreement, to kick in from 2020.

If the roadmap were accepted, it would mean that all the world's major emitters – both developed and developing countries – would negotiate a new pact in 2015 to cut emissions from 2020 onwards.

From now until 2020, most of the world's governments – including all of the biggest emitters – are covered by their own national emissions-cutting targets. But these are voluntary and not legally binding, in the way the Kyoto protocol is. Although some governments, including the US, are happy to continue with a voluntary system, the EU and many developing nations are concerned that it is too open to political meddling, and allows countries too easily to renege on their commitments – and that could harm the climate. They are pushing for the new post-2020 agreement to be legally binding.

The US is unhappy with agreeing so far in advance that the outcome of years of negotiations should be legally binding, and China has long refused to take on international legally binding commitments while insisting that developed countries should do so, arguing that the rich world bears responsibility for most of the stock of emissions now in the atmosphere.

The EU was confident that it had the support of more than 120 countries, including major developing economies such as Brazil, South Africa, Argentina, many African countries and the world's least developed economies in pushing the deal through. However, under UN rules, every country must agree the text of any agreement for it to be passed.