China has unilaterally opened a third extension of the controversial M503 civil aviation route near the Taiwan Strait, sparking strong criticism from Taipei and escalating regional tensions. The new W121 extension, unveiled on July 6, 2025, now permits west-to-east civil flights from mainland China towards Taiwan. This development comes hot on the heels of Taiwan's upcoming Han Kuang military exercises, designed to simulate responses to a potential Chinese blockade or invasion.

Taiwan's Mainland Affairs Council, in a statement to Pilotcenter.net News, condemned China's move as an unjustified attempt to disrupt the status quo in the strait, labeling it a threat to regional stability. The council emphasized the importance of joint discussions for any modifications to the M503 route and its extensions.

While China argues that this extension enhances airspace efficiency, reduces delays, and benefits passengers on both sides, Taiwan remains wary. This marks the third extension following the activation of W122 and W123 in 2024. The approval of the M503 route by the International Civil Aviation Organization in the mid-2000s aimed to alleviate congestion on China's A470 route, but its proximity to the strait's median line has long raised security concerns in Taipei.

Amidst escalating tensions under Taiwan's Democratic Progressive Party, China's actions regarding the M503 route are seen as part of broader attempts to undermine the island's de facto sovereignty through a mix of civil and military pressure. Despite initial concessions made by Beijing in 2015, recent years have witnessed a rollback of those measures, causing further strain in cross-strait relations.