Top US trade and energy officials said Thursday they were confident China and the United States would step up cooperation on climate change after meeting with Chinese leaders.

US Trade Secretary Gary Locke and Energy Secretary Steven Chu, both ethnic Chinese, came to China seeking to open the Asian giant's markets to US green technology while urging Beijing to set hard targets on gas emissions.

"Secretary Chu and I measured the success of this trip by answering the simple question of whether America and China can increase their cooperation in the development... of clean energy and energy efficient technologies," Locke told reporters.

"After three days of meeting, the simple answer is yes."

During the trip, China and the United States -- the world's largest emitters of greenhouse gases -- announced the establishment of a joint clean energy research centre aimed at allowing scientists from both sides to work together.

The centre, with headquarters in both countries, is also intended to serve as a clearing-house for information, with key issues initially to be looked at including energy efficiency, clean coal technology and low-polluting cars.

Locke and Chu met with Chinese Premier Wen Jiabao on Thursday afternoon, with the environment, as well as a host of trade and other issues, on the agenda. They also held talks individually with other top officials.

Their visit to China comes as officials prepare for the first US-China strategic and economic dialogue, to be held in Washington next week.

It also comes ahead of a UN meeting in Copenhagen in December when more than 180 nations are due to negotiate a new climate agreement to replace the existing Kyoto Protocol.

China and other developing nations are refusing to agree to compulsory cuts in emissions under the new deal, saying developed countries must shoulder the responsibility for the decades of emissions that have led to global warming.

But the US officials in China have been trying to convince Chinese leaders that the world has no choice but to work together more closely.

Chu said he was optimistic about the upcoming climate talks after meeting with Chinese officials.

"China... recognises the serious consequences that they face, as well as the world, if the world -- China included -- doesn't start to take aggressive action," Chu said.

"I am optimistic of what is going to be happening in Copenhagen."

During a visit to China last month, US climate change negotiator Todd Stern sought to get China to commit to accepting slow increases in its greenhouse gas emissions until it hit a "peak year," beyond which a real decrease must occur.

But Beijing has refused to agree to any compulsory targets.

Chinese foreign ministry spokesman Qin Gang indicated the visit by Locke and Chu had no impact on China's climate change policy.

"The most important point is to stick to the principal of common but differentiated responsibilities to cope with the challenges faced by the international community on climate change," Qin told reporters.

Without such cuts from China, the US Congress will be hard pressed to pass a bill setting its own cuts, US officials have said.

Congress is considering legislation that would reduce greenhouse gas emissions by 17 percent from 2005 levels by 2020, and 83 percent by 2050.

China has said that such cuts are not enough and that developed nations must make a bigger effort.