About a month before Taiwan's January presidential election, China began sending intruders over the Taiwan Strait: more than 100 balloons, some of which passed through the island's airspace or busy, Taipei-controlled air corridors for civil aviation.
Experts say the balloons could be psychological warfare, carry surveillance tools or simply gather meteorological data. On some days, as many as eight were detected within a few hours; at other times, weeks passed without any balloons at all. In the week leading up to Taiwan's presidential election on Jan. 13, an average of three balloons were spotted each day.
Then on April 11, they stopped altogether.
The increased frequency has raised alarms both domestically and abroad.
A senior Taiwanese security official briefed on the matter said Chinese balloon flights near Taiwan took place on an "unprecedented scale" in the weeks leading up to Taiwan's elections and described the incidents as part of a Chinese pressure campaign – so-called grey-zone warfare designed to exhaust a foe using irregular tactics without open combat.
Taiwan inaugurates its new president, Lai Ching-te, on May 20. China, which views democratically governed Taiwan as its own territory despite the island's objections, has a strong dislike of Lai, believing him to be a dangerous "separatist", whose repeated offers of talks it has rejected, including one in May.
China's defence ministry did not respond to a request for comment.
China's Taiwan Affairs Office referred Reuters to its comment on Jan 31, in which it dismissed complaints about the balloons, saying they were for meteorological purposes and should not be hyped up for political reasons.
Before Dec 8, balloon data was not public, making historical comparisons impossible.
But Jan Jyh-horng, the deputy head and spokesperson of the Mainland Affairs Council, Taiwan's top China policy-making body, told Reuters that in the past, a balloon would be spotted "maybe once a month".
Between December 2023 and April 2024, more than four balloons were detected on eight separate days. In total, just over a hundred balloons were flown during that period.
Three Taiwanese officials briefed on the matter confirmed that the number of Chinese balloons had increased significantly in recent months. The majority are weather balloons collecting atmospheric data, including wind, temperature and humidity, they said, but Taiwan still sees them as Chinese harassment.
The balloons have flown at an altitude of 11,000 to 38,000 feet, with a mean altitude of 22,294 feet – well under the usual altitude for meteorological balloons. According to the US National Weather Service, weather balloons typically reach altitudes of more than 100,000 feet.
"Sending them over at that kind of altitude is dangerous," said Alexander Neill, strategic adviser on Indo-Pacific geopolitics formerly at the International Institute for Strategic Studies and the Royal United Services Institute. "You are within air traffic corridors, and the potential for a collision is concerning."
Jan agreed, saying the balloons are threats to aviation safety.
"They fly very slowly while planes move speedily," he said. "It could be too late when they were spotted, if they were sucked into the engines."
China's most frequent form of "grey zone" activity has been the almost daily air force and navy missions in the waters and skies around Taiwan, forcing the island's armed forces to repeatedly scramble to see off the intruders.
Other tactics Taiwanese officials have expressed concern about include sand dredging close to the Taiwan-controlled Matsu islands, which sit near the Chinese coast.
A second senior Taiwanese senior security official said, citing intelligence gathered by Taiwan, that the data potentially collected by the balloons would be useful for the PLA's rocket forces, because atmospheric factors could affect missile launches.
"If China was planning to mount an air assault onto Taiwan, they would need to understand the meteorological conditions and wind patterns of the island," Neill said.
Wang Ting-yu, a senior lawmaker for Taiwan's ruling Democratic Progressive Party and chair of parliament's foreign affairs and defence committee, told Reuters balloons are hard for military radars to detect unless their sensitivity is set to high levels.
But ultra-sensitive radars are likely to spot objects such as birds, and as a result, Taiwan's military might miss other vital targets such as incoming missiles.
"It's a challenging task," he said.
Raymond Kuo, director of the RAND Corporation's Taiwan Policy Initiative, says he thinks the purpose of the balloons is primarily psychological.
"I personally am sceptical of what additional intelligence China could get from balloons that they couldn't get from other platforms," Kuo said. "I think they're mostly meant to signal to Taiwan that they can't even defend their airspace."
