Shanghai Pudong Airport closed for 2hrs to clear air traffic
From Ming Pao newspaper and Appledaily newspaper of HongKong:
Yesterday, Shanghai Pudong International Airport (PVG) and Hongqiao Airport (SHA) closed for 2 hrs from 2pm to 4pm to clear the congested sky around the airport. Consequently, many incoming flights were diverted to nearby cities such as Nanjing and Hangzhou. The reason for the closure was not announced initially, so for many passengers and crews, the airport just seemed to have shut down without reasons. Affected flights included 27 flights between HongKong and Shanghai (either delayed, diverted or cancelled). Japanese media also reported that 2 JAL flights (one passenger and one cargo) had to return to Tokyo after learning of the airport closure.
In any case, it seems strange to close the country's busiest airport to "clear congestions". The diverted flights have to return to PVG, so I don't really see how it would relieve congestions.
But the news reports say that there are also other sources saying it's due to military exercises.