Senator John Kerry, on track to be America's next secretary of state, told US lawmakers on Thursday that he would work to boost ties with China, but warned of a "long slog" ahead.

Kerry told his Senate confirmation hearing that he wanted to "grow the rebalance" towards Beijing "because it is critical to us to strengthen our relationship in China."

Washington would continue the so-called pivot -- begun during the first term of President Barack Obama -- towards Asia and in particular China, Kerry told the Senate Foreign Relations committee, though he added that America was not "turning away from anywhere else."

Kerry said that while the United States and China would remain economic "competitors," the two nations "shouldn't be viewed as adversaries in some way that diminishes our ability to cooperate on a number of things."

"China is, you know, the other sort of significant economy in the world and obviously has a voracious appetite for resources around the world, and we need to establish rules of the road that work for everybody," Kerry said.

He acknowledged the difficulty of issues such as intellectual property rights, and China's propping up of its currency, the yuan. But he stressed there were areas where the two economic superpowers could work together.

"China is cooperating with us now on Iran. I think there might be more we could perhaps do with respect to North Korea," the veteran senator said.

"There could be more we could do in other parts of the Far East. And hopefully we can build those relationships that will further that transformation. We make progress. It's incremental... It's a tough slog."

Another area where the two nations could perhaps come together might be on climate change, Kerry added. Earlier in the hearing he had vowed to be "a passionate advocate" on the subject of working to battle global warming.

"China is soon going to have double the emissions of the United States of America. So we've got to get these folks as part of this unified effort, and I intend to work very, very hard at trying to do that," Kerry said.

But he appeared to rule out any move towards increasing again the US military force in the Asia-Pacific region.

"I'm not convinced that increased military ramp-up is critical yet," Kerry said, adding that if confirmed he wanted to "dig into this a little deeper" and try a thoughtful approach.

"We have a lot more bases out there than any other nation in the world, including China today," he argued, saying the Chinese must be wondering "What's the United States doing? They trying to circle us? What's going on?"