The surveillance balloon effort, which has operated for several years partly out of Hainan province off China’s south coast, has collected information on military assets in countries and areas of emerging strategic interest to China including Japan, India, Vietnam, Taiwan and the Philippines, according to several U.S. officials, who, like others interviewed for this story, spoke on the condition of anonymity because of the matter’s sensitivity.Officials have said these surveillance airships, operated in part by the PLA air force, have been spotted over five continents.“What the Chinese have done is taken an unbelievably old technology, and basically married it with modern communications and observation capabilities” to try to glean intelligence on other nations’ militaries, said one official. “It’s a massive effort.”

On Monday, Deputy Secretary of State Wendy Sherman led a briefing on China’s balloon espionage for some 150 people from about 40 embassies, said a senior administration official familiar with the matter. The department has also sent to every U.S. Embassy a “detailed information” on the espionage that can be shared with allies and partners.Separately, U.S. officials have begun to share specifics with officials in countries such as Japan whose military facilities were targeted by Beijing.“There has been great interest in this on the part of our allies and partners,” said a senior administration official.

In Japan in 2020, an aerial orb drew speculation. “Some people thought this was a UFO,” said a Japanese official. “In hindsight people are realizing that was a Chinese espionage balloon. But at that time it was purely novel — nobody had seen this. … So there’s a lot of heightened attention at this time.”

Analysts still don’t know the size of the balloon fleet, but there have been “dozens” of missions since 2018, said one U.S. official.