According to International Union of Public Transport (UITP), Tokyo has the busiest metro system, followed by Moscow and Shanghai. Among top 10, China made four including Beijing, Guangzhou and Hong Kong.

People in the wagon of line 1 of Shanghai metro. (Photo: VCG)

UITP is a nonprofit organization that promotes public transport worldwide. Beijing followed Shanghai in the fourth place, followed by Guangzhou in the eighth place and Hong Kong in the tenth.