A surge in sightings of balloons from China flying over Taiwan has drawn the attention of the island’s military and struck some experts as a calculatedly ambiguous warning to voters weeks before its presidential election.

Taiwan’s Ministry of National Defense has reported occasional sightings of balloons floating from China since last month, and a surge in recent days, according to the ministry’s daily tally of Chinese military activities near the island. Official Taiwanese accounts about balloons were previously very sporadic.

The recent balloons have mostly stayed off Taiwan’s coast. On Monday, however, one flew across the island, according to the ministry’s descriptions of their paths. Of four spotted on Tuesday, three flew over Taiwan, and two passed through to the island’s east side, facing the Pacific Ocean. Another flew over the island on Wednesday.

The Taiwanese reports also noted some of the balloons’ proximity to the island’s military bases. Of the four reported on Tuesday, three were first detected 120 to 184 miles from the Ching Chuan Kang Air Base in the city of Taichung. Taiwan’s defense ministry declined to specify how close to the base they may have flown.