ISTANBUL

China has issued a 40-day shutdown notice for offshore airspace without providing an explanation, according to a report by The Wall Street Journal on Sunday.

The alerts are in effect from March 27 through May 6 and have not previously been reported, the media outlet said.

The zones China reserved cover an area larger than Taiwan’s main island, including offshore airspace north and south of Shanghai. They stretch from the Yellow Sea facing South Korea and south to the East China Sea facing Japan, according to the US Federal Aviation Administration.

Similar alerts issued in the past were used to warn aviation authorities of Chinese military exercises, which usually last just a few days, the report said.

However, Beijing has not announced any exercises in the area, "sparking a new aviation mystery following an unexplained pause in military flights around Taiwan."

Beijing conducted massive drills around the island at the end of last year.

The airspace reserved in the current alerts lies hundreds of miles from Taiwan.

While civil aviation appears unaffected, coordination is needed for aircraft to transit such areas. The reserved airspace also has no vertical ceiling.

There was no reaction from Beijing to the report at the time of publication of this report.