Flying to and from Beijing? Bring your patience. The city's aviation hub remains the most delayed international airport in the world.

Beijing Capital International Airport ranked bottom in the on-time performance report in June, with just 18.3 percent of commercial passenger flights leaving on schedule. Shanghai Pudong International Airport reported the second worst departure record at 28.72 percent, among 35 major international airports.

The report was released by FlightStats, a US service that tracks historical and real-time flight information around the globe.

Tokyo's Haneda maintained its top spot, with an on-time performance of 95.04 percent.

A flight is considered "on time" if it arrives or departs within 15 minutes after its scheduled take-off or landing time.

There have been different voices from China's industry insiders over air traffic volume as the cause of flight delays.

Civil aviation occupied only 20 percent of air traffic in China, with 80 percent of the flow for military use, while the situation in the US was the opposite, said Wang Junjin, president of Juneyao Airlines in Shanghai.

China's air space would be crowded with just over 10,000 operating flights per day, but over 60,000 operating flights per day compete to fly in the US and could still maintain order, Wang added.

An opposing view says air traffic should not be blamed for flight delays. China's airports couldn't keep up with the growth of commercial aircrafts, said Zou Jianjun, an associate professor at the Civil Aviation Management Institute of China.