Beijing on Friday hit out at a US intelligence agency report accusing the Chinese of extensive cyber spying, saying it was unprofessional and irresponsible.

The unusually blunt report on foreign cyber spying submitted to the US Congress on Thursday said the Chinese were the world's "most active and persistent perpetrators" of economic espionage.

"Cyber attacks are transnational and anonymous," Chinese foreign ministry spokesman Hong Lei told reporters.

"Without investigation, to prejudge the origin of the attack is neither professional nor responsible."

The report was compiled by the office of the National Counterintelligence Executive, which is responsible for defending against foreign intelligence threats to the United States.

It said cyber spies were interested in information and communications technology, business information, military technologies, particularly marine systems and drones, and medical and pharmaceutical secrets.

While emphasising that it was difficult to prove state sponsorship in cyberspace, the report said "Chinese actors are the world's most active and persistent perpetrators of economic espionage.

"US private sector firms and cybersecurity specialists have reported an onslaught of computer network intrusions that have originated in China, but the (US intelligence community) cannot confirm who was responsible," it said.

Between 2009 and 2011, "computer networks of a broad array of US government agencies, private companies, universities, and other institutions -- all holding large volumes of sensitive economic information -- were targeted by cyber espionage," the report said.

"Much of this activity appears to have originated in China," it said, adding that Russia’s intelligence services were also conducting activities to collect economic information and technology from US targets.

Hong said China hoped the international community would "discard prejudice and work together with the Chinese side to maintain cyber security."