China has pledged for the first time to take firm action to tackle climate change, telling a UN summit it will to curb emissions by 2020.

Vice-Premier Zhang Gaoli said China's carbon emissions - the world's highest - would soon peak.

US President Barack Obama said climate change was moving faster than efforts to address it, and the US and China had a responsibility to lead other nations.

The summit was the largest high-level climate meeting since 2009.

Hosted by UN Secretary General Ban Ki-moon, it aimed to encourage 120 member states to sign up to a comprehensive new global climate agreement at talks in Paris next year.

As he closed the summit, Mr Ban hailed the meeting, saying "never before have so many leaders gathered to commit to action on climate change".

The UN has previously warned that the impacts of global warming are likely to be "severe, pervasive and irreversible", leading to problems such as sea level rises, greater flood risks and changes to crop yields.

Mr Zhang told the summit China would aim to cap emissions or have them peak "as early as possible".

"As a responsible major country, a major developing country, China will make even greater effort to address climate change and take on international responsibilities that are commensurate with our national conditions and actual capabilities," Mr Zhang said.

"All countries need to follow the path of green and low carbon development that suits their national conditions, [and] set forth post-2020 actions in light of actual circumstances."

Correspondents say this is the first time China has said it is willing to take firm action to cut carbon emissions.

However, Chinese President Xi Jinping was not at the summit, held before the formal start of the UN General Assembly session.

Speaking earlier, Mr Obama said that he had spoken to Mr Zhang, with the pair agreeing that the world's two biggest emitters "have a responsibility to lead", but that all nations must play a part.

The "urgent and growing threat of climate change" would ultimately "define the contours of this century more dramatically than any other" issue, he added.

(BBC)