On the third day of his visit to China, Panetta flew to the eastern port of Qingdao, home to the headquarters of the Chinese navy's northern fleet, becoming the first Pentagon chief to set foot in the facility.

Chinese officers promised Panetta a tour of one of their newer frigates and diesel submarines, a day after he spoke at a military engineering academy in Beijing.

In his speech to cadets and young officers, Panetta sought to reassure them that the US strategic tilt to the Pacific was not to curtail China's power but an effort to promote stability in an area vital to the global economy.

"Our rebalance to the Asia-Pacific region is not an attempt to contain China. It is an attempt to engage China and expand its role in the Pacific," Panetta said Wednesday.

"It's about creating a new model in the relationship of our two Pacific powers."

The Chinese navy's latest warships and submarines are the subject of intense scrutiny by US military strategists, defence analysts and American lawmakers.

They worry about Beijing's increasing focus on precision-guided ballistic and cruise missiles that could render an array of bases and aircraft carriers vulnerable in key waterways.

The growing rivalry with China is driving plans in Washington to fund  stealth fighters electronic jamming equipment and other hardware.

But the effect of Beijing's military spending is open to debate, with some sceptics accusing the American defence industry and lawmakers of overstating China's military prowess.

For its part, China has questioned America's plans, criticising proposals to deploy Marines to Australia and shift more ships to Southeast Asia.

During his visit, Panetta has adopted a conciliatory tone, offering to work with Beijing as a partner to address common threats such as natural disasters or piracy.

Panetta's week-long Asia tour, which started in Japan on Sunday and will wrap up in New Zealand, came at a delicate time with tensions soaring between Beijing and Tokyo over disputed islands in the East China Sea.