Four people including a former Boeing engineer and US Defense Department weapons expert were held on Monday on suspicion of stealing Space Shuttle secrets and spying for China.

It's a serious breach of national security and it showed China's spying efforts are approaching Cold War levels, said the US Justice Department.

The engineer was arrested at his home in Orange County, California, on allegations he supplied trade secrets from several aerospace programs including the Space Shuttle.

Don fang Greg Chung, 72, was an employ of Rockwell International from 1973 until its defense and space unit was acquired in 1996 by Boeing.

It is alleged that Chung gave China, Boeing secrets about the Space Shuttle, C-17 military transport aircraft and the Delta IV rocket.

In another incidence, two men and a woman including a US Defense Department official were alleged to have given classified US government documents to China.

Tai Shen Kuo, 58, and Yu Xin Kang, 33, both from Orleans, Louisiana were charged with conspiracy to disclose national defense information to a foreign government while Gregg Bergersen, 51, of Alexandria, Virginia, a US weapons systems policy analyst, was accused of conspiracy to disclose national defense information to persons not entitled to receive it.

Berger and Kuo will appear in a federal court in Alexandria on Tuesday, while Kang will appear before a federal court in New Orleans.

Those who compromise classified national security information betray the enormous responsibility and trust placed in them by our government and the American people, said US Attorney, Chuck Rosenberg.

According to the court documents, the offences were committed between January 2006 and February 2008.