President Xi Jinping told a group of US and Chinese officials on Tuesday that the two countries "should take advantage of the opportunities brought by their enormous economies".

"Size itself means business opportunities," Xi said in Seattle at the third China-US Governors Forum as he started his state visit to the US. "The two countries' status as the world's two largest economies is a bonanza of opportunity for Chinese provinces and US states to explore for cooperation."

China and the US also should take advantage of each other's development, Xi said. The forum focused on clean energy and economic development and a low-carbon approach.

Xi emphasized the importance of subnational cooperation, noting grassroots support plays an important role in developing the country-to-country relationship.

"Ultimately, we need the support from the people, and our relationship will serve the people in the end.

"In recent years, the subnational relationship between US states and Chinese provinces has grown rapidly - there are so far 43 provinces and states in a friendship relationship and 200 sister cities.

"Secondly, the two sides should share the favorable policies of each other's reform and development," Xi said.

"The US is making efforts in economic restructuring to stimulate economic resurgence," he said.

"Some states have taken quite some approaches to attract investment, which are even more favorable than ours in the 1980s. This will create opportunities for cooperation.

"We encourage more Chinese provinces to seek high-level exchanges and cooperation in the US to realize self-development and also benefit the local communities," Xi said

"The relationship between China and the US in the past 30 years has benefited tremendously from the strong support it receives from the two peoples and governments, and in the future the two nations will work together to strengthen ties and make best use of the great opportunities generated from the robust bilateral economic exchanges," he said.

Xi also called for closer cooperation between China and Washington state when he met with the governor, members of the state Senate and Assembly and the mayor of Seattle.

"I have come to the United States to deepen friendship between our two peoples, expand practical cooperation across the board and bring about even greater progress in the building of the new model of major-country relationship between China and the United States," Xi said.

In 2013, Xi and US President Barack Obama met in Sunnylands, California, and reached a consensus to build a new model of major-country relationship between China and the US, one of no-conflict, non-confrontation, mutual respect and win-win cooperation.

Xi said Seattle and Washington are important gateways to China and Asia. He reviewed the history of Liu Lin Hai, a vessel of the China Ocean Shipping Group Co that sailed into the Port of Seattle in April 1979, the first Chinese-flag ship to call on a US port since the founding of the People's Republic of China.

"It marked the start of US-Chinese maritime relations. Now Washington state has the largest exports to China among all the states in the US," he said. "For the future, the city of Seattle as well as Washington state need to work together with China to 'change gear and speed up' for cooperation and development."

He said both governments and cities need to work on cooperation, provide support and connections, and boost economical and cultural exchanges. Xi also said he expected further cooperation and mutual development in sectors such as manufacturing, biotechnology and environmental protection.

US representatives at the meeting included Washington Governor Jay Inslee, Seattle Mayor Ed Murray, US Congressman Rick Larsen, and former Washington governor and US ambassador to China Gary Locke.

They said they were honored to welcome Xi to Seattle and Washington, noting that the state has a long history of good relations with China.

Lia Zhu in Seattle contributed to this story.