The new lines would expand the national rail network to 120,000 kilometres within the next five years - an increase of over 30 per cent on the 91,000 kilometres currently in use.

Besides the rail network, dozens of mainland cities are racing to build or expand subway systems at a frenzied pace before their roads become congested with cars.

Across the mainland, massive tunnel boring machines are working overtime and workers working in 12-hour, five-day-a-week shifts to build some of the world's largest subway systems.

Last year, Shenyang in Liaoning and Foshan in Guangdong both launched underground rail networks, and new lines in Hangzhou in Zhejiang, and Xian in Shaanxi are due to open this year.

Metro systems are under construction in at least 14 other mainland cities - from Qingdao in Shandong to Nanning in Guangxi - due to be running by 2017.

There are plans on the drawing board for subway networks in at least 16 other cities.

Cities with subway systems already running are also attempting to expand their coverage. Just last week, Beijing opened five new metro lines on the same day, increasing its network to 13 lines.

Shanghai is already home to the world's longest subway network, with 420 kilometres of track on 11 lines already operational.

By the end of the decade, however, a further nine lines are scheduled for completion, bringing the total up to 877 kilometres.

However, experts have begun to question the logic behind such rapid development and whether the massive investment involved would be cost effective.

Chinese Academy of Engineering Professor Wang Mengshu told the Shandong Business Daily that although subway systems were an effective means to alleviate the pressure on the above-ground transport network, he feared the pace of construction was being driven by inter-city rivalry to build 'the longest [network] in the shortest time'.

Wang's concerns reflect questions raised in Shanghai last year when a collision between two trains on the city's underground in January sparked debate about the pace of its construction.

Although no one was injured in the incident, which occurred when the driver of an empty train ignored signal lights, rescuers needed more than three hours to reach stranded passengers, and the crash threw the city's transport system into chaos.

Safety concerns about the system - on which delays and stoppages are a regular occurrence - were given another jolt in July when a female passenger was crushed to death after being caught between a train's doors as they closed.

Shanghai officials privately admit that technical troubles on the subway are partly due to the breakneck speed at which the system has been constructed.

With subway manufacturers struggling to keep up with the demand for new trains, the city was forced to use a variety of different engineering systems.

As a result, rolling stock is compatible only within individual lines, and engineers need to receive training specific to each of the systems while maintenance staff cannot work on other lines.

Growth track

The Beijing to Shanghai line is part of a vast and growing network

New lines will expand the national rail network to this many kilometres within the next five years: 120,000