"That is a trend that we are seeing," Dennis Blair, the US national intelligence director, told congress, adding it was unclear whether Beijing was using its growing power "for good or pushing people around".

On Monday US defence officials said five Chinese ships surrounded and harassed the unarmed navy vessel in international waters on Sunday.

At one point they said a Chinese ship had come within 8 meters of the Impeccable strewing debris in its path.

The Impeccable's crew resorted to spraying one Chinese vessel with water from fire hoses to force it away, officials at the Pentagon said.

But despite the impact of the water, Chinese crew members stripped to their underwear and continued closing in.

'Dangerous proximity'

The USNS Impeccable is designed to detect and track undersea threats [AFP/US navy]
A statement from the US defence department said the ships "shadowed and aggressively manoeuvred in dangerously close proximity" to the navy ship in international waters 120km south of China's Hainan Island.

The incident is the latest in a series of confrontations between US surveillance craft and Chinese coastal defences

The US Embassy in Beijing said a protest had been lodged with the Chinese foreign ministry as well as with the Chinese Embassy in Washington.

It said the Impeccable had been conducting "routine operations in the South China Sea in accordance with customary international law."

"The actions of the Chinese vessels put both sides at risk and are inconsistent with the obligation for ships at sea to show due regard for the safety of our ships," the statement said.

"Our Navy will continue to operate in international waters in accordance with customary international law and we expect China to exercise due regard for the safety of our ships."

Chinese claims

The Impeccable is one of five US navy surveillance ships designed to use sonar to compile information the navy can use to steer its own submarines or track those of other nations.

China views almost the entire South China Sea region as its territory – a claim which has put it at odds with at least five South-East Asian nations.

Based on its claim, Beijing has argued that any intelligence gathering by foreign governments within its exclusive economic zone is illegal.

The US and other nations however say that only exploitation of economic resources such as undersea gas deposits is restricted.

Tensions last spiked between the Chinese and US militaries in 2001 when a US spy plane and Chinese fighter jet collided in international air space off Hainan.

The pilot of the Chinese jet was killed while the US plane was forced to make an emergency landing at a Chinese air base.

The crew of the plane and the aircraft itself were only returned to the US after several days when Washington delivered a carefully-worded apology to Beijing over the incident.