According to officials, similar surveillance balloons have been operating partly out of Hainan province off China’s south coast and collecting valuable military data, including in Japan, India, Vietnam, Taiwan, and the Philippines. The officials added that China's balloons 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... It’s a massive effort," one of the officials said.

According to officials, Washington has begun to brief allies and partners who have been allegedly targeted by China's spy balloons. In particular, the media cited a senior administration official as saying that Deputy Secretary of State Wendy Sherman led a briefing on China's balloon espionage for some 150 people from about 40 embassies on Monday.

"There has been great interest in this on the part of our allies and partners... Many of them recognize that they, too, may be vulnerable or susceptible to this or an object of interest to the PRC [the People's Republic of China]," the official said.

Last week, a high-altitude Chinese balloon, which the Pentagon says was conducting surveillance, was spotted over the United States before a fighter jet shot it down on Saturday.

China argued the airship was engaged in scientific research, but the incident nevertheless sparked a diplomatic row, including the postponement of a visit by Secretary of State Antony Blinken to Beijing.

(With UNI inputs)