Taiwan's defense ministry says it detected four balloons from China crossing the median line of the Taiwan Strait, with three of them flying above the main island.

The ministry said on Wednesday that it spotted the balloons from morning through evening on Tuesday.

The ministry gives a daily update on Chinese military aircraft that have been spotted near Taiwan over the past 24 hours. Last month, it also began to report the number of balloons that flew from China.

All the balloons the ministry reported in December were detected over the surrounding waters. But the ministry confirmed balloons flew above Taiwan's main island for two days in a row since the beginning of the year.

The ministry had said until Tuesday that it believed the balloons were for weather monitoring, but did not give a view in Wednesday's update.

Some observers in Taiwan speculate that the series of balloon incidents are Beijing's attempt to put pressure ahead of Taiwan's presidential election scheduled for Saturday next week.

Taiwan's defense ministry says it has been aware that the number of balloons flying from China tends to increase in winter due to wind direction.

Officials said that the ministry began a daily report on balloons to let people in Taiwan know that they are keeping an eye on the situation, and to reduce opportunities for China to spread misleading information.