President Xi Jinping delivers a speech for the opening day of the World Climate Change Conference 2015 (COP21) at Le Bourget, near Paris, France, November 30, 2015. [Photo/Xinhua]

China will formally ratify the Paris Agreement before September, said Vice-Premier Zhang Gaoli, who signed the climate agreement on behalf of President Xi Jinping on Friday at a special ceremony at the United Nations.

Zhang, Xi's special envoy, also called on all G20 members to give early approval to the agreement.

"China will finalize domestic legal procedures on its accession before the G20 Hangzhou summit in September this year," said Zhang to applause from the audience.

More than 175 countries signed the agreement on Friday. It was a new record for the most countries to sign an international agreement on one day, which had been set in 1982 when 119 countries signed the Law of the Sea Convention.

"Today is a day that I have worked toward since day one as secretary-general of the United Nations and declared climate change to be my top priority. Today you are signing a new covenant with the future," said UN Secretary-General Ban Ki-moon, who will step down at the end of this year after 10 years in the post.

"Today's record-breaking number of signatures on the climate change agreement sends a powerful message to the international community. It's now time to take action for humanity," said Ban.

The signing is the first step toward ensuring that the agreement reached in Paris last December goes into force. The next step will be for each nation to unilaterally ratify the agreement, which in many cases will involve passage by national legislatures.

"We will work with the rest of the international community for early accession to the agreement and to be sure it's early entry into force," said Zhang.

With his granddaughter on his lap, US Secretary of State John Kerry signed the agreement. "The United States looks forward to formally joining this agreement this year," he said. "We call on all of our international partners to do so."

It reaffirmed the joint commitment to tackle climate change by China and the US, which account for 38 percent of the world's greenhouse gas emissions.

"China has set the target of achieving the peak of CO2 emissions around 2030, making the best effort to peak earlier," said Zhang.

China plans to decrease its CO2 emissions by 18 percent in the second half of the decade, according to the 13th Five-Year Plan. The government will control total energy consumption and carbon intensity, pushing for near-zero emission demonstration projects and establishing a nationwide carbon market.

"We will deepen the South-South cooperation on climate change," said Zhang. China will launch new projects under the new South-South Cooperation Climate Fund this year to help other developing countries.

Ban has always praised such effort. "We must support developing countries in making this transition. The poor and most vulnerable must not suffer further from a problem they did not create," he said during his speech.