Negotiators on Wednesday tiptoed through a problem-laden draft for a UN climate pact amid deepening concern over a December deadline to seal the deal.

Just one day is left in a key round of talks intended to propel 195 countries towards an historic accord in Paris just over six months from now.

But after 10 days' haggling, observers said almost nothing has been done to demine a text stuffed with political explosives.

"There has been too much time spent fiddling around with the unimportant details of the text," Christian Aid's Mohamed Adow said.

"Negotiators have acted like schoolchildren colouring in their homework timetable and not getting around to any actual homework."

The goal is a post-2020 agreement that will reduce the threat of climate change for future generations.

It would limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels, fending off crippling droughts, floods, storms and rising seas.

But the draft agreement, sprawling over nearly 90 pages, reflects the position of every single country, with many views in direct contradiction to others.

The Bonn meeting has focused on maintaining consensus, by surgically removing duplicated text or finding laborious compromise on some of the less contentious wording.

The tough decisions will ultimately be made by ministers and heads of state, as negotiators have no mandate to make political concessions.

But without a manageable text to give their bosses, deadlock could result, as was notoriously the case at the 2009 Copenhagen summit -- the last time UN members tried to forge a climate treaty.

"We are gravely concerned about the progress of the negotiations and would like to express our utmost disillusionment on the mistrust reigning in the corridors," said Mithika Mwenda of the campaign group Pan African Climate Justice Alliance.

"We challenge the parties to effectively utilise the remaining few hours to agree on something concrete that will illuminate some hope to millions of people waiting for signals that this will cease to be an endless game of musical chairs."

The potential time bombs in the text are many.

One of the biggest is how to encourage countries to crank up their pledges of carbon cuts, and monitor that they honour their promises.

"Ambition is ultimately a question of political will, but the Paris agreement must have strong design features to help drive it up over time," said Tony de Brum, foreign minister of the Marshall Islands, which supports a five-yearly review.

Also in dispute are basic questions such as the agreement's long-term goal and financial help for developing countries.

- Loss and damage -

Still undetermined, too, is a mechanism to compensate poor countries for damage incurred due to unavoidable man-made global warming.

"The overwhelming level of harm being felt in developing countries comes from emissions in developed countries, so there is an issue of responsibility there," said Gita Parihar of Friends of the Earth.

Measures could include a compensation fund and relocation of climate refugees.

But these issues can only be determined in head-to-head bartering.

"Negotiators are in danger of wasting their last hours, avoiding real progress on the substance of the Paris climate deal," Adow said.

"It's time to put the colouring pens away and really get down to work. They must create a clear list of options which can be worked out by ministers before the next (negotiating) session in Bonn in August."