At least 20 airports in east China are now experiencing flight delays or cancellations on a large scale this week.

The Civil Aviation Administration of China was forced to issue a red alert yesterday afternoon.

Red is the highest alert for flight disruptions.

PLA drills mean flight delay misery for many

Shanghai's two airports, Pudong and Hongqiao, remain the most affected, with 160 flights cancelled and another 40 delayed through yesterday.

China's air traffic regulators contend bad weather is the main reason for the delays, arguing the military drills currently taking place in parts of central and eastern China are having only limited impact on civil aviation.

Zhou Qing with China Eastern Airlines is warning passengers to prepare for long delays.

"China Eastern Airlines has already planned ahead and cancelled 19 flights. We have completed rebooking procedures with the affected passengers. The passengers will depart on their new flights in an orderly manner. "

As a result of the air-traffic delays, many passengers have switched to trains, making tickets - particularly in Shanghai - hard to come by.

"I came here for a meeting. I arrived last night. My flight was on time last night. But this morning when I watched the news, it said a lot of flights would be cancelled. So I booked a train ticket instead."

Officials have warned the delays are likely to affect flights in eastern and central China until mid-August.