China Railway's high-speed 'Harmony' bullet trains are seen at a high-speed train maintenance base in Wuhan, Hubei province, early December 25, 2012 [Photo/Agencies]

In the six years since China opened its first high-speed rail line, total mileage of the network has equaled the sum of the rest of the world.

By the end of last year, the country's system had grown to 15,000 km of dedicated track, connecting 28 of its 34 provincial regions.

China's railway builders have also taken their plans global - a line to Western Europe is planned as well as already exporting rail technology and bullet trains.

The scale of the project is massive, but critics worry about corruption, safety and the price tag.