Several airports including Beijing and Guangzhou reported a system failure around 1-2 pm.

Hong Kong was affected from around 5 am until 7 pm. The airport authorities there said 37 out of 644 flights were delayed, on average for about 30 minutes. Chengdu Shuangliu International Airport was also hit.

The reason for the computer breakdown was still unknown last night .

Domestic departure passengers could not get electronic boarding passes because of the system failure.

"We applied our emergency plan and asked staff to issue boarding passes and do check-in manually," said Ma Ruzhuang from the Beijing Capital International Airport.

The system failure also meant luggage weight could not be counted, which could affect flight safety, said Ma. Therefore, all the affected 33 flights in Beijing had to wait for the system to recover, he said.

Hu Yejun, from Guangzhou Baiyun International Airport's publicity department, said the departing system became paralyzed about 1.30 pm. He said the airport initiated manual operations for check-in and boarding procedures.

"More than 20 flights were slightly influenced by the system failure."

In Hong Kong, electronic screens failed to display flight information.

Most airlines there resumed normal check-in procedures at 8:30 am. But some still had not had the problem fixed much later.

Hu in Guangzhou said the airport encountered a similar problem in January the departing system was paralyzed for about 20 minutes.

The computer system is managed by the TravelSky Technology Limited.