SHANGHAI - Passenger numbers at China's airports hit 620.5 million in 2011, up 10 percent year-on-year, the country's civil aviation authorities said.

Passenger traffic at four airports located in three of the country's metropolises -- Beijing, Shanghai and Guangzhou -- accounted for 32 percent of total airport traffic, according to a report released by the Civil Aviation Administration of China (CAAC) on its website late Wednesday.

The number of airports with annual passenger numbers exceeding 10 million reached 21, up from 16 in 2010, accounting for 75.1 percent of total airport traffic, said the report.

China had 180 airports in 175 of its cities at the end of 2011, excluding Hong Kong, Macao and Taiwan.

Total cargo volume at those airports rose 2.5 percent year-on-year to 11.6 million tons, it said.

Moreover, the country has 47 airports with annual cargo throughput of more than 10,000 tons. Airport cargo traffic at those airports accounted for 98.6 percent of the country's total in 2011, according to the report.

China plans to invest more than 1.5 trillion yuan ($238 billion) in the aviation industry by 2015 to meet surging demand as its economy booms, Li Jiaxiang, head of the CAAC, said last year.

By 2015, the country is expected to have more than 220 airports, he said.