February 7th, 2012
10:50 AM GMT
Hong Kong (CNN) – Hong Kong is one of the most densely populated places on the planet.
In a place like this, one of the greatest challenges is getting people from A to B.
The city's main subway carries 4 million passengers a day. This key piece of infrastructure is being expanded.
CNN's Richard Quest goes beneath the city streets to find out how it will be done.