European Union leaders warned it would be tough to seal a high-stakes climate change deal as they began talks today on a pact aimed at making Brussels a global trailblazer for decades to come.

The two-day EU summit will focus on an ambitious package of climate change targets for 2030 but also tackle the Ebola crisis, economic stagnation and the crisis in Ukraine.

But deep divisions over the cost of the climate measures were holding up a deal, especially from coal-reliant Poland, and key targets remained in doubt even as leaders of the 28 nations arrived for the summit.

"The negotiations won't be easy and I can't say if there will be a result," German Chancellor Angela Merkel told reporters.

The EU wants to agree on what would be some of the world's toughest climate change targets ahead of a summit in Paris in 2015, at which a new UN-backed global treaty is to be agreed.

EU nations broadly agreed on two key areas: binding targets to cut greenhouse gas emissions by 40 percent over 1990 levels and to make renewable energy such as solar and wind power account for 27 per cent of energy, sources told AFP.

But a third major benchmark for energy efficiency was a bigger headache, with negotiators proposing a non-binding target of 27 per cent for energy efficiency only at the last minute on Thursday, they said.

EU leaders had yet to confirm those targets and the talks could go on late into the night.

French President Francois Hollande said a deal was "in view" and that he was doing everything possible with Germany and Britain to secure a deal, but acknowledged that "there is one country at the moment which is resisting."

"If there is no agreement in Brussels between the most advanced countries on this issue, how can we convince the Chinese, the Americans or poorer countries?" he told reporters.

Hollande did not name the hold-out country, but Poland's pointman on climate issues, Marcin Korolec, said on Twitter today that a "deal is still quite far away. Final work begins now."

Poland's prime minister Ewa Kopacz has previously threatened to veto a deal, with her country's heavy reliance on coal meaning it would be expensive to convert power plants to meet the climate targets.

Countries like Portugal and Spain are at odds with France over their desire to build more cross-border cables to export surplus electricity produced by wind power.