The United States and China yesterday pledged to work together to fight climate change and promote free trade as they set the stage for an era of closer cooperation between the Pacific giants.

The world's largest developed and developing nations wrapped up two days of in-depth talks in Washington to chart out the future of their relationship, which President Barack Obama said would shape the 21st century.

The two nations - by far the biggest emitters of carbon blamed for global warming - signed a memorandum putting the fight against climate change at the heart of their ties. While short on specifics, the two sides said they would put in place a committee on environmental cooperation aimed at smoothing the rocky path toward a new global treaty on climate change in Copenhagen in December.

"Today's agreement should send a clear signal that the United States and China are ready to work together on clean energy and climate change and sets the stage for what I hope will be many years of close cooperation," US Energy Secretary Steven Chu told a signing ceremony at the State Department. China's State Councilor Dai Bingguo said that the US and China "have important contributions to make" to contain climate change, which UN scientists forecast will put entire species at risk if unchecked.

"We hope that through our joint efforts we will be able to expand common ground and cooperation," Mr Dai said.

However, Mr Dai stressed that the two countries had "big differences" in their stages of development and historical responsibilities for climate change.