China has stepped up computer espionage against the US government and American businesses, according to an influential Washington congressional panel.
In its annual report to Congress, the panel warned that China was gaining increasing access to sensitive information from US computer networks.
It said China was aggressively pursuing cyber-warfare capabilities to gain an advantage over the US in any conflict.
There has been no comment so far from the Chinese on the report.
The US-China Economic and Security Review Commission was set up by Congress in 2000 to advise, investigate and report on US-China issues.
It alleges that the Chinese are looking for diplomatic and military secrets in government databases, and potentially lucrative industrial secrets held by American corporations.
The report said the US government and economy were critically vulnerable to cyber-space attack since both depended heavily on computers and the internet.
The panel of six Democrats and six Republicans said China would continue to target the US using cyberspace as it was cheaper and less risky than traditional espionage activities.
Another advantage, they say, is that determining who infiltrated computer networks is often difficult to establish.
"China is stealing vast amounts of sensitive information from US computer networks," said Larry Wortzel, chairman of the commission.
His panel recommended that lawmakers should provide funds for US government agencies - including those run by the military and homeland security - that would monitor and protect sensitive information held on computer networks.
The panel also warned the expansion of Beijing's space programme was making the US more vulnerable.
Chinese satellite technology now lets its military locate US navy ships more quickly and accurately than ever before.
The Chinese authorities have not so far commented on the commission's findings.
But officials in Beijing have responded to past reports by saying China does not try to undermine other countries' interests and seeks healthy ties with the US.
The BBC's Richard Lister in Washington says relations between the US and China have remained fairly steady in recent years, but this report suggests the impact of Beijing's growing power and influence should now be re-assessed.