The mainland’s first aircraft carrier, the Liaoning, sailed north through the Taiwan Strait on July 12, wrapping up a five-day visit to the Hong Kong Special Administrative Region, the haiwainet.cn reported, citing Taiwan media. The transit was greeted with alarm by Taiwanese authorities, who pledged to monitor the vessel and its escorts.

China's Ministry of National Defense has not confirmed the transit as of press time.

According to Taiwanese officials, Liaoning’s transit through the sensitive strait took place at around 2:40 am on July 12. The vessel entered Taiwan’s “air defense identification zone,” staying on the west side of the strait’s centerline. Many experts believe that the sail-by was not a provocation, as the vessel did not sail on the east side of the centerline.

This is not the first time that the aircraft carrier has entered the strait. On July 1, three days after the U.S. government approved a $ 1.4 billion arms package for Taiwan despite the mainland’s protest, the vessel entered the strait en route to Hong Kong for a first-ever visit as part of China’s celebrations marking the 20th anniversary of the former British colony’s handover back to China.

The aircraft carrier along with several other vessels set out from Qingdao in east China on June 25 for a routine training mission. The naval formation includes the advanced 052C and 052D destroyers. According to the national defense ministry, the training mission, like previous ones, is expected to improve overall coordination and improve the skills of crew and pilots in different marine regions.