Chinese hackers have accessed designs of nearly 70 US weapons systems, including those for Patriot missiles and Black Hawk helicopters.

The revelations made in a Defense Science Board report give details of 37 breached programmes, including the F-35 Lightning II.

Britain is buying 48 of the new Anglo-American fighter-bombers, which are being tested by Royal Navy engineers in the US.

It also includes the Terminal High Altitude Area Defense weapon - a land-based missile defence system that was recently deployed to Guam to help counter the North Korean threat.

Other programmes include the F-22 Raptor fighter jet and the hybrid MV-22 Osprey, which can take off and land like a helicopter and fly like a plane.

The report also listed another 29 broader defence technology projects that have been compromised, including drone video systems and high-tech avionics.

While officials have been warning about the problem with Chinese cyber attacks for years, the breadth of the list underscores how routine they have become.

The disclosure heightens fears that the knowledge could be exploited by China in a conflict and blunt America's growing military presence in the Asia Pacific region.

James Lewis, a cybersecurity expert at the Center for Strategic and International Studies, said: "It introduces uncertainty on how well the weapons may work, and it means we may have to redo weapons systems.

"If they know how it works precisely, they will be able to evade it and figure out how to better beat our systems."

President Barack Obama has come under intense pressure to crack down on China’s cyber espionage, and is expected to discuss the issue with Chinese President Xi Jinping during a meeting next week.

In November 2011, a report by US intelligence agencies accused China of systematically stealing American high-tech data for its own national economic gain.

The Pentagon, meanwhile, in its latest report on China’s military power, said publicly for the first time that Beijing’s military was likely to be behind computer-based attacks targeting federal agencies.

"In 2012, numerous computer systems around the world, including those owned by the US government, continued to be targeted for intrusions, some of which appear to be attributable directly to the Chinese government and military," said the report, which was released earlier this month.

Cyber security experts have urged the government to use sanctions or other punishments against China for the breaches.

The benefits of cyber espionage are high and the costs are low, said Shawn Henry, former cyber director at the FBI.

"There is no cost, there are no sanctions, no diplomatic actions, no financial disincentives," he said, adding that the US intellectual property losses are in the hundreds of millions of dollars.

He said the US needs to have a discussion with Chinese leaders about "what the red lines are and what the repercussions will be for crossing those red lines".

US leaders, including Mr Obama, however, have instead been using the bully pulpit to increase pressure on the Chinese to confront the problem.

Pentagon officials are playing down the report.

Pentagon Press Secretary George Little said: "We maintain full confidence in our weapons platforms.

"Suggestions that cyber intrusions have somehow led to the erosion of our capabilities or technological edge are incorrect."