The men are suspecting of selling secret information to Beijing that included manuals for warships and their weapons systems, as well as blueprints for a radar system and plans for a huge US military exercise.

"These arrests are a reminder of the relentless, aggressive efforts of the People's Republic of China to undermine our democracy and threaten those who defend it," said Suzanne Turner of the FBI's Counterintelligence Division, which was involved in the sting.

China "compromised enlisted personnel to secure sensitive military information that could seriously jeopardize US national security."

In a press release, the Department of Justice said sailor Jinchao Wei, who served on the amphibious assault ship the USS Essex in San Diego, had handed over dozens of documents, photos and videos detailing the operation of ships and their systems.

These included technical and mechanical manuals that dealt with the weaponry of his own vessel.

The 22-year-old, who is alleged to have been paid thousands of dollars for the information, faces possible life in jail if convicted.

In a separate case, the DoJ said Petty Officer Wenheng Zhao, 26, had spied for China for nearly two years from his perch at Naval Base Ventura County, north of Los Angeles.

Zhao is alleged to have been paid almost $15,000 by a Chinese intelligence agent for information about a large-scale US military exercise in the Indo-Pacific, including details on the timing and location of amphibious landings.

He is also alleged to have handed over electrical diagrams and blueprints for a radar system at a US military base in southern Japan, where the United States has a large military presence.

"By sending this sensitive military information to an intelligence officer employed by a hostile foreign state, the defendant betrayed his sacred oath to protect our country," US Attorney Martin Estrada said.

"Unlike the vast majority of US Navy personnel who serve the nation with honor, distinction and courage, Mr. Zhao chose to corruptly sell out his colleagues and his country."

If convicted, Zhao faces up to 20 years in jail.