Hongtudi station, which opened on Line 6 years ago, was dubbed Chongqing muncipalitiy's deepest station at 60 metres below ground. Now, it is being extended deeper to connect with Line 10, a new metro line to be opened by the end of 2017.
Chongqing is known as a "mountain city" in China. Because of the hilly terrain and to avoid damaging air-raid shelters and pile foundation of street buildings, the station has to be built deep underground.
The station's 32 elevators will be increased to 91 when it becomes a transfer station, state-run Xinhua news agency reported.
In recent years, Chongqing is speeding up the construction of its subway system as the increasing number of vehicles on the road has caused traffic jams.
Many Chinese cities are pushing forward the development of rail transit systems. Figures from the National Bureau of Statistics showed that China had 4,153 kms of urban rail networks in operation across 30 cities until last year.