PHNOM PENH -- Passengers from China and Thailand are driving double-digit annual growth in Cambodia's airport traffic, local media reported on Monday, citing a report from the Center for Asia Pacific Aviation.

A total of 6.47 million travellers passed through Cambodia's three international airports in Phnom Penh, Siem Reap City and Sihanoukville last year, a 13 percent increase from 2014 and the sixth successive year of double-digit growth.

"China has been the biggest driver...with Chinese visitor numbers increasing by at least 20 percent for six consecutive years," the Cambodia Daily quoted the report as saying.

"Capacity on the traditional route to Bangkok, the main gateway for long-haul passengers heading to or from Cambodia, has also grown over the last year."

Sinn Chanserey Vutha, deputy director-general of Cambodia's State Secretariat of Civil Aviation, said a swelling middle class in China, Thailand, Vietnam and Laos was behind the growing number of tourists and business people visiting the country.

"We have seen that middle-income populations have expanded globally and throughout the region," he was quoted as saying by the newspaper.

The report also notes an increase in seat capacity for flights to and from China and Thailand, thanks to the launch of new airlines and more frequent scheduled flights.