Three Chinese hot air balloons flew over the island of Taiwan on Tuesday and flew past an air base, Taiwan’s defense ministry said, according to Reuters.

China’s potential to use balloons for espionage became a global concern in February 2023 when the United States shot down what it said was a Chinese surveillance balloon. China said the balloon was a civilian craft that accidentally went astray.

Before the presidential and parliamentary elections on January 13, Taiwan is in a state of heightened readiness for Chinese activities, both military and political. China considers the island its territory.

Taiwan’s defense ministry has reported several incidents since last month of Chinese balloons flying over the sensitive Taiwan Strait, then crossing into airspace north of the island before disappearing.

On Wednesday, in its daily report on China’s military activities over the past 24 hours, the ministry said it had detected four balloons flying over the strait, three of which flew over the center of the island.

The three flew 105 nautical miles (194 km), 160 nautical miles and 159 nautical miles, respectively, southwest of Chin Chuan Kang, home to an important Taiwan Air Force base, he said.

The balloons then disappeared at various points, added the ministry, which previously said it believed they were mainly for weather monitoring.

Asked whether the latest balloons were used for meteorological or other purposes, the ministry declined to comment.

According to the ministry, it “monitors the balloons closely and reacts appropriately” and collects information about their route for “judgment and analysis”.

Over the past four years, China has stepped up its military activity around Taiwan, and Chinese warplanes and warships now regularly operate in the strait.