China and the United States, the world two largest greenhouse gas emitters, will announce on Tuesday major climate actions at the sub-national levels following a landmark climate agreement reached last November in Beijing.

The cities, countries, provinces and states from the two countries attending the US China Climate Leaders Summit in Los Angeles on Tuesday will sign a climate leaders declaration to take parallel steps to address climate change, a senior Obama administration official said on Monday. He called the declaration "first of a kind".

Chinese cities will announce the formulation of an alliance for peaking pioneer cities. And all the cities and provinces in that alliance will announce for the first time their peak years, a year to peak CO2 emissions, earlier than the national goal of peaking around 2030.

During President Obama's trip to Beijing last November, the two countries announced a major climate deal. The US pledged to reduce its emissions by 26-to-28 percent below its 2005 level in 2025 and to make best efforts to reduce its emissions by 28 percent, while China vowed to achieve the peaking of CO2 emissions around 2030 and to make best efforts to peak earlier.

"This is important because the commitment to early peaking by so many mega cities in China highlights that the country as a whole is moving to achieve its national target as early as possible, which is consistent with that commitment China made to make its best effort to peak earlier than 2030," the official said.

For example, Beijing and Guangzhou are committed to peak their emissions at around 2020, 10 years earlier than the 2030 national targets.

Chinese cities and provinces that are making these early peak commitments represent 1.2 gigatons of annual CO2 emissions in aggregate, roughly the CO2 emission levels of Japan or Brazil.

He called it a "big deal in signaling progress towards the overall national goal."

In the declaration, US cities, counties and states are also making new or reaffirming pledges to make dramatic emission reductions, including from the state of California to reduce emissions by 80-90 percent by 2050, and a commitment by the city of Seattle to become entirely carbon neutral by 2050.

"Just at the high level, we are very excited about this summit and the progress that it represents," the official said in a background briefing.

"This will be the first of a host of productive exchanges that allow our sub-national actors — cities, states and provinces — to exchange ideas, exchange experiences, and importantly make partnerships and commitments to drive our respective countries to achieve the climate outcome that we are committed to."

While saying the ambitious targets set last November have put the two countries in the leadership role on climate change this year, the official noted that this year needs to be a year of implementation, a year that the two countries demonstrate their commitments to implementing and executing those goals, with ambitious, concrete steps to reduce their carbon emissions in a way to move their economies forward.

Chinese State Councilor Yang Jiechi, as a special representative of President Xi Jinping, will travel to Los Angeles for the summit, also known as the first China-US Summit on Climate-Smart/Low Carbon Cities from Sept 15-17.

US Special Envoy for Climate Change Todd Stern will also travel there to represent the US Department of State.

The climate declaration is likely to be viewed as proof that China and the US can collaborate on important global issues despite their differences, a positive message ahead of the upcoming state visit to the US by President Xi later this month.

The sub-national actors in China and the US are not only committing to ambitious targets, they are also committing to regularly report their greenhouse gas emissions and establish a climate action plan to reduce emissions as well as to increase bilateral partnerships between themselves, according to the official.