China and the United States launched a joint initiative to protect the oceans, highlighting such cooperation as proof the two nations can work together despite stubborn disagreements.

US Secretary of State John Kerry and State Councilor Yang Jeichi chaired the first meeting of a new oceans working group, on the third and final day of key annual talks between Beijing and Washington.

"Once again we're breaking new ground with respect to China and the United States' ability to find an area in which we can cooperate, which has major significance... for people everywhere," Kerry said.

Some 400 Chinese officials have been visiting Washington since Sunday for the yearly strategic and economic dialogue, a forum for the two uneasy partners to try to manage their increasingly complex ties.

China and the United States are two of the top fishing nations in the world, Kerry said, and also leaders in ocean science.

"So we have a real opportunity here to be able to come together... to deal with conserving and protecting the oceans," he said, adding it could be "a centerpiece in the newly defining relationship with China."

Even though the world's two leading economies remain at odds over some aspects of maritime policy -- in particular Beijing's territorial claim to most of the South China Sea -- Kerry said "in the marine environment there is an urgent need for our countries to step up and help lead."

Beijing and Washington are working together to try to create a marine protected area in Antarctica in the Ross Sea, he said, referencing one of the world's last true wildernesses.