China has sealed off a portion of its coastal airspace for 40 days — an unprecedented measure carried out without any explanation.
Beijing designated part of its coastal airspace as a reserved zone, the Wall Street Journal reported Monday. The alert, known as a Notice to Airmen (NOTAM), took effect from March 27 through May 6.
The measure resembles military exercise warnings that typically last only a few days. However, China has not announced any drills in the designated zone. Military flights around Taiwan have also been suspended without explanation. The restricted airspace is located hundreds of miles from Taiwan.
China notified pilots and aviation authorities of temporary airspace hazards and restrictions. The closure is not expected to directly affect commercial aviation, though prior coordination is required for flights passing through the zone.
"What's particularly notable is the unprecedented 40-day duration and the absence of any announced exercise," said Ray Powell, head of Stanford University's Gordian Knot Center for National Security Innovation's SeaLight project. "This suggests sustained operational readiness rather than a one-off drill, and China doesn't seem to feel the need to explain."
The restricted zone includes coastal airspace north and south of Shanghai and is larger than the main island of Taiwan, according to U.S. Federal Aviation Administration (FAA) data. It stretches from the Yellow Sea facing South Korea to the East China Sea near Japan.
A senior Taiwanese security official assessed that China is actively projecting its military presence, citing the fact that the alert was issued immediately after U.S. airstrikes on Iran. Earlier, after the Trump administration approved an $11 billion (approximately 15 trillion won) arms sale to Taiwan, the Chinese military conducted large-scale drills around Taiwan in late December last year. At the time, China named the exercise "Joint Sword-2025A" and called it "a stern warning against Taiwan independence separatist forces and external interference forces."
Ben Lewis of PAX Tracker, a research group that monitors Chinese military activity, said China has issued at least four similar NOTAMs along the same coastline over the past 18 months, but they typically lasted three days. "Given that Kuomintang Chairman Eric Chu is visiting China this week and President Trump's visit to China is approaching next month, the likelihood of a major drill or escalation is low for now," he said.
Meanwhile, a U.S. congressional delegation recently visited Taiwan, Japan, and South Korea, urging swift approval of military budgets to bolster defense capabilities through weapons purchases.