U.S. airports used to be the busiest in the world, but passenger air travel in Asia has exploded in recent years, to some extent dwarfing traffic in the west, according to a new report.

Airports Council International (ACI) has released its annual ranking of busiest airports in 2017 and, as has been the trend in recent years, airports in Asia -- particularly China and India --have supplanted U.S. airports in terms of passenger traffic.

Of the top 20 busiest airports for passenger travel ranked by ACI, only five were in the U.S. Nine of the airports were located in Asia, four were in Europe and two were in the Middle East. In 2000, by comparison, 13 U.S. airports were in the top 20 list, followed by five in Europe. In Asia, only Tokyo and Seoul, South Korea, made the list.

Reflecting the growth of the industry in Asia, one of the new airports on the top 20 list in 2017 was Indira Gandhi International Airport in New Delhi, which was 16th on the list with 63.4 million passengers served, up 14 percent from 2016.

"Growing rapidly in a relatively short period of time, India is poised to be one of the largest aviation markets in the world in the years to come," the ACI report stated. "With an astounding population base of over 1.3 billion inhabitants, the move towards a more liberalized aviation market coupled with stronger economic fundamentals has helped to awaken the Bengal tiger to become one of the fastest growing markets in the world."

The report also noted that China was the world's largest contributor to growth in air passenger and cargo volumes, with more than 10 airports that each serve more than 20 million passengers per year. "The growth of Chinese aviation has also boosted international traffic on market segments with other regions such as North America," the report stated.

The U.S., however, continued to hold the top spot in the busiest airport ranking.

The following airports, in ascending order, were identified as the top 10 busiest in the world for passenger traffic:

10. Paris-Charles De Gaulle Airport, France
France's famed airport is the second largest in Europe. It served 69.4 million passengers in 2017, which was a 2.3 percent increase.