Top American diplomat John Kerry said Tuesday the relationship between the United States and China was the "most consequential" in the world today, warning it needed to be "carefully managed."

Ties between the two powerful economies will "do much to determine the shape of the 21st century," Kerry said, before leaving on what will be his fourth trip to China since becoming secretary of state 21 months ago.

The two major powers "have a profound opportunity to set a constructive course on any number of issues, from climate change to global trade," Kerry insisted.

"For that reason, our relationship has to be carefully managed and guided, not by news hooks and grand gestures, but by a long-term strategic vision, by hard work, by good diplomacy and by good relationships."

Shortly after speaking, Kerry left on a new diplomatic trip, heading first for Paris where he will meet French Foreign Minister Laurent Fabius.

He will then fly to Beijing to join Asia-Pacific foreign ministers and lay the groundwork for the annual APEC summit hosted by Chinese President Xi Jinping and to be attended by US President Barack Obama in China next week.

America's China policy was founded on two pillars, Kerry told an audience at the Johns Hopkins University School of Advanced International Studies.

The goals were "constructively managing our differences -- and there are differences -- and just as constructively coordinating our efforts on the wide range of issues where our interests are aligned."

But Washington was not giving Beijing a free pass when it came to voicing differences over regional tensions or human rights, Kerry stressed.

"We do not simply agree to disagree when it comes to maritime security, especially in the South and East China Seas," he insisted, referring to Beijing's territorial claims to vast swaths of the two seas.

"We take a strong position on how those claims are pursued and how those disputes are going to be resolved," he said, adding the US was "deeply concerned" by the mounting regional tensions.

On the issue of cyber-hacking and the theft of intellectual property by Chinese authorities and industry, Kerry said Washington had been equally firm.

"We've been very clear about how strongly we object to any cyber-enabled theft of trade secrets and other sensitive information from our companies," he said.

And he pledged the United States would continue to press China's communist authorities to respect human rights and freedom of speech, including in Hong Kong.

- Shared responsibility -

But even though "our differences will undoubtedly continue to test the relationship," the two nations should be able to cooperate on a wide range of issues, and not just on economic and trade ties.

"There is both opportunity and necessity to coordinate our efforts to address global security concerns. Our shared efforts to respond to the global threat of climate change are a perfect example," Kerry said.

China and the United States are the world's two largest energy consumers, and the biggest emitters of greenhouse gases, blamed for global warming, and therefore had a "shared responsibility" to seek solutions through a wise energy policy.

"The solutions are within reach. But they will require ambitious, decisive and immediate action," Kerry said.

The top US diplomat will also visit Oman on this trip, where he will meet with Iranian Foreign Minister Mohammad Javad Zarif as a deadline for a deal on Iran's nuclear program looms.

He will then fly back to Beijing to accompany Obama.