(Bloomberg) -- A flurry of Chinese weather balloons crossed Taiwan for the first time since the island began releasing such data, as tensions with Beijing flare ahead of the self-ruled democracy’s presidential election this month.

Four balloons were spotted between 8:27 a.m. and 6:41 p.m. Tuesday, the Defense Ministry in Taipei said in a statement. They continued traveling northeast and disappeared, with three crossing the island, the ministry added.

On Monday, a Chinese balloon flew over Taiwan for the first time since the ministry started publishing balloon sightings last month. The authorities previously said they had long been spotting the craft without making the information public. 

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The trespassing came as Taiwan prepares to go to the ballot box on Jan. 13, in an election that will shape cross-strait ties. President Xi Jinping reiterated on Sunday that China will “surely be reunified” — an allusion to Taiwan, which is also a major flashpoint between the world’s largest economies.

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Last year, a Chinese balloon that drifted over the US derailed ties between Beijing and Washington for months. President Joe Biden’s administration said the aircraft was for surveillance and shot it down. China said it was for weather purposes.

The ministry in Taipei said it will closely monitor and check if there are other usages for these balloons besides sounding, and pledged to take appropriate measures. It will collect the patterns of their flying paths for analysis.

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