Twenty countries including Britain, Canada and New Zealand have joined an international alliance to phase out coal from power generation before 2030.

The Powering Past Coal Alliance was unveiled at the COP23 climate talks in Bonn, Germany, which were working out the technical details of the 2015 Paris Agreement.

"I think we can safely say that the response has been overwhelming," Canadian Environment Minister Catherine McKenna said.

"There is so much momentum, there is so much ambition in this room."

The alliance, which isn't legally binding, was launched days after a pro-coal presentation by the Trump administration jarred with many ministers who wanted the talks to focus on cleaner energy sources.

Included countries: Angola

Angola Austria

Austria Belgium

Belgium Britain

Britain Canada

Canada Costa Rica

Costa Rica Denmark

Denmark El Salvador

El Salvador Fiji

Fiji Finland

Finland France

France Italy

Italy Luxembourg

Luxembourg The Marshall Islands

The Marshall Islands Mexico

Mexico The Netherlands

The Netherlands New Zealand

New Zealand Niue

Niue Portugal

Portugal Switzerland

Australia isn't part of the alliance, which also doesn't include some of the world's biggest coal users China, India, the United States, Germany and Russia.

Coal is responsible for more than 40 per cent of global emissions of the greenhouse gas carbon dioxide.

"Around the world we see close to a million deaths a year from air pollution created by burning coal," Ms McKenna said.

"Not only is there a human cost, there is also a huge economic cost totalling billions of dollars a year."

Since signing the Paris Agreement, several countries had already made national plans to phase out coal from their power supply mix.

The Powering Past Coal Alliance also involves sharing technology to reduce emissions, such as carbon capture and storage, and encouraging the rest of the world to cut usage.

The alliance aims to have at least 50 members by the next UN climate summit in 2018 to be held in Poland's Katowice, one of Europe's most polluted cities.

"I hope the room will have to be four times bigger in Katowice, but we are off for a good start," British Environment Minister Claire Perry said.

Meanwhile, the United States told the talks it is committed to reducing greenhouse gas even though the Trump administration still plans to pull out of the Paris Agreement.

In her closing remarks to the conference, the US State Department's Judith Garber said:

We remain open to the possibility of rejoining [the Paris Agreement] at a later date under terms more favourable to the American people."

The US states of Washington and Oregon have already signed up to the Power Past Coal Alliance.

ABC/wires