From March 27 to May 6, Beijing issued a series of aviation alerts known as Notice to Airmen, or NOTAMs, covering wide areas of the Yellow Sea and East China Sea.

According to The Wall Street Journal, the restricted zones form a long north-south corridor off the coast near Shanghai, stretching between waters facing South Korea and Japan.

What makes this move unusual is not just the scale, but the duration.

Chinese military exercises typically last only a few days. This time, the warning period extends to 40 days, with no official explanation and no publicly announced drills.

China’s Ministry of National Defense and Civil Aviation Administration have not commented.

Experts say the details of the airspace designation are key. Ray Powell of Stanford University notes the zones are marked “surface to unlimited altitude,” with no vertical ceiling. Combined with the extended timeframe, he says it suggests not a single exercise, but a sustained state of operational readiness. If linked to military activity, Powell says it could signal a shift in how Beijing uses airspace control to send strategic messages.

China Military & Indo-Pacific Security Expert Christopher Sharman says the reserved zones could allow pilots to rehearse air combat maneuvers for potential conflict scenarios.

The development follows a brief pause in Chinese military flights near Taiwan, as U.S. attention shifted to the Middle East. Officials say the move may also be aimed at deterring Japan and other U.S. allies in the Indo-Pacific.