US President Barack Obama has announced a climate deal in Copenhagen with other major world leaders, calling it "unprecedented" but still not enough to beat global warming.

His announcement came more than four hours after the scheduled close of the summit and an exhaustive round of diplomacy between the US, China and India.

US officials say the agreement includes a commitment from wealthy and key developing nations to limit global warming to two degrees Celsius.

Mr Obama said he would leave the Danish capital before the 194-nation summit takes a final vote on the accord, which he called "meaningful".

"This progress did not come easily and we know this progress alone is not enough," he said.

"Climate change threatens us all, therefore we must bridge all divides," he said.

"The time has come for us to get off the sidelines and shape the future we seek.

"That's why I believe what we have achieved in Copenhagen will not be the end, but the beginning."

The United States, China, India and South Africa have agreed on the text of what will be known as the Copenhagen Accord.

If the 194-nation summit votes for the accord, it will be a statement of intent, not a legally binding treaty.

Correspondents say the breakthrough appears to have come after a US backdown on wording on verification procedures.

French President Nicolas Sarkozy says all countries have agreed to the deal.

"We have an agreement," Mr Sarkozy told a news conference in Copenhagen after the meeting of 120 world leaders.

"The text we have is not perfect."

Mr Sarkozy says Germany will host a new conference on climate change in six months in Bonn, to follow up the work of the Copenhagen summit.

The final outcome will be sealed at a conference in Mexico City at the end of 2010.

Under the accord, he said all countries - including China - would have to submit written plans for curbs in carbon dioxide emissions by January 2010.

He said all countries had signed up for a plan to provide developing nations with $US100 billion a year in aid by 2020.

China's top climate negotiator Xie Zhenhua said the summit had a positive result and that all should be happy.

"After negotiations both sides have managed to preserve their bottom line, for the Chinese this was our sovereignty and our national interest," he told reporters.

Step towards binding treaty

Mr Obama described the document as a step towards drawing up a legally binding treaty.

"The way this agreement is structured, each nation will be putting concrete commitments into an appendix to the document," he said.

"Those commitments will then be subject to an international consultation and analysis.

"It will allow for each country to show to the world what they are doing. We'll know who is meeting and who is not meeting the mutual obligations set forth.

"We know they will not be by themselves sufficient to get to where we need to get by 2050."

Mr Obama said while a legally binding agreement would be neccessary in the future, it was important for progress to be seen to be made.

"This is a classic example of if we just waited for that [a legally binding agreement], then we would not make any proccess," he said.

"And I think there would be such frustration that instead of taking one step forwards, we would take two steps back."

But he warned that the cuts needed to halt global warming cannot be ignored and should not be lost in the debate.

"But this will ultimately be driven by the science, and the science indicates we're going to have to take more aggressive steps in the future," he said.

"I want to make sure that whatever it is we can promise we can actually deliver on."

- ABC/AFP/Reuters