BEIJING (Reuters) - China's Parliament on Saturday (Sept 3) ratified the Paris agreement on climate change, the Xinhua state news agency said, which could help put the pact into force by as early as the end of the year.

The standing committee of China's National People's Congress voted to adopt "the proposal to review and ratify the Paris Agreement" at the closing meeting of a week-long session, the news agency said.

The announcement came as leaders from the world's 20 biggest economies, the Group of 20 (G-20), began to arrive in the Chinese city of Hangzhou for a summit on Sunday and Monday.

The G-20 nations are responsible for about 80 per cent of global carbon emissions. The United States, the second biggest emitter, is also set to ratify the agreement in a bid to put the deal into legal force before the end of the year.

Nearly 200 countries agreed in Paris in December on a binding global compact to slash greenhouse gas emissions and keep global temperature increases to "well below" 2 deg C.

Experts have said the temperature target is already in danger of being breached, with the UN weather agency saying that 2016 is on course to be the warmest since records began, overtaking last year.

While 180 countries have now signed the agreement, 55 nations - covering at least 55 per cent of global emissions - need to formally ratify the treaty to put it into legal effect.

Before China, 23 nations had ratified it - including North Korea - but they collectively accounted for just 1.08 percent of global emissions, according to the UN Framework Convention on Climate Change.

China is responsible for just over 20 per cent of global emissions while the United States covers another 17.9 per cent. Russia accounts for 7.5 per cent, with India pushing out 4.1 per cent.

Countries that ratify the deal will have to wait for three years after it has gone into legal force before they can begin the process of withdrawing from it, according to the agreement signed in Paris last year.