BEIJING (AFP) — US House of Representatives speaker Nancy Pelosi said Tuesday that the fight against climate change was a "game changer" in China-US relations, as she visited Beijing on a trip focused on energy.

Pelosi, a tough critic of China's human rights record and a vocal advocate of environmental protection, is leading a delegation from the US Congress to China on a working visit devoted to energy and climate change.

"I think that this climate change crisis is a game changer in US-China relations, it is an opportunity that we cannot miss," she said at a clean energy forum in Beijing.

Delivering a speech at the meeting, which aims to find ways for the United States and China to cooperate on clean energy, Pelosi linked the issue of human rights to environmental justice.

"We see the thread of workers' rights, human rights, people's rights, and environmental justice -- a principle that must be upheld as we go forward," she said.

Speaking at the same forum, US Senator John Kerry -- who is on a separate trip to China -- said the success of a key UN environment summit in Denmark in December rested largely on China and the United States.

"I personally believe that the success of Copenhagen can be defined by what China and the United States agree on over the course of the next few weeks," he told reporters.

The Copenhagen meeting is set to hammer out a new climate treaty to replace the Kyoto Protocol when it expires in 2012.

Kerry said a number of US officials, including President Barack Obama's top science adviser and the designated negotiator for climate change, were coming to China in the next weeks to work towards an agreement on emissions.

"If two countries -- powerful economies like China and the United States -- are creating about 50 percent of all the world's emissions, obviously what these two countries decide to do will have a profound impact on the rest of the world," he said.

According to some measures, China has surpassed the United States as the world's top emitter.

Pelosi arrived in China on Sunday with the delegation where she visited one of China's most influential Catholic priests in Shanghai and toured the financial district.

Her visit comes just over a week before the 20th anniversary of the 1989 bloody government crackdown on pro-democracy protesters in and around Tiananmen Square.

But like US Secretary of State Hillary Clinton, who visited China in February, Pelosi has not yet made any public statements about human rights.

Kerry's trip to China is focused on climate change, as well as nuclear non-proliferation issues concerning North Korea and Iran.