China issued sudden alerts warning that parts of its airspace are restricted (Picture: AFP/Getty Images)

China has mysteriously blocked parts of its airspace for 40 days without a warning.

The world’s second most populous country announced it will restrict five areas of airspace on its northeastern coast.

While China didn’t give a reason for the sudden move,it is believed to suggest possible military action in the area.

Beijing reportedly issued alerts in force from March 27 until May 6.

These alerts are similar to the ones used to warn civilian aviation authorities about military exercises,according to the Wall Street Journal.

Previous drills have not lasted for longer than a few days.

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Start your day informed with Metro's News Updates newsletter or get Breaking News alerts the moment it happens.China has restricted its airspace in the past,but rarely for more than a few days (Picture: China News Service/Getty)The alerts,known as ‘Notice to Air Missions’ (Notams),are designed to give a heads-up to air traffic controllers about hazards on the usual flight path in a specific area.Today,the Chinese airspace appeared unaffected by the alerts,with the flight tracking website Flightradar24 showing a steady flow of aircraft,including in the northeast.The zones,named SFC-UNL,have no vertical restriction,meaning technically China has restricted the airspace column up to space.The reserved airspace extends for around 340 miles from the Yellow Sea to the East China Sea off the coast of Shanghai,the US aviation watchdog,Federal Aviation Authority,said.Though the restricted zone is not near Taiwan,it has raised questions over Beijing’s intentions.Taiwanese Air Force’s fighter jet seen taking off from Hsinchu Air Base on December 29,the same day China launched major military exercises around the island (Picture: AFP/Getty Images)Beijing sees Taiwan as a breakaway province of China,and it has not hidden its hopes to take over the island one day.Despite the tense relationship between Taiwan and China,which have no diplomatic relations currently,American spies said Beijing is not planning to invade the island.Ray Powell,the director of maritime tracking project SeaLight at Stanford University,told the WSJ: ‘What makes this especially notable is the combination of SFC-UNL with an extraordinary 40-day duration—and no announced exercise.‘That suggests not a discrete exercise but a sustained operational readiness posture—and one that China apparently doesn’t feel the need to explain.’Get in touch with our news team by emailing us at .