Beijing was the first city on the Chinese mainland to build a metro system, and there are now 18 lines covering a total distance of 527 kilometers. The total is scheduled to reach around 1,000 kilometers by 2020 to meet the huge demand from the capital's population of more than 21 million. The expansion should ease traffic congestion and reduce air pollution.

The cost of materials, labor, machinery and land acquisition and resettlement has also continued to rise, and this has pushed up the amount of investment needed, the company said.

Metro construction projects in other cities have also been affected by rising costs. It is estimated that at least 3 trillion yuan will be invested nationwide in networks that will cover a total distance of 6,000 kilometers by 2020, official Li Guoyong told China Business Times. Li works in the infrastructure projects section of the National Development and Reform Commission, the country's top economic planning agency.

There are currently two companies involved in running the capital's network－city-owned Beijing Mass Transit Railway Operation Corp, and Beijing MTR Corp, a public-private joint venture with Hong Kong's MTR.

On Feb 8, Beijing MTR Corp paid 15 billion yuan for the right to operate Line 16 for 30 years. It already runs Line 4 and Line 14.

Safety is a major concern both during the construction process and after new lines open.

Le Guiping, a spokesman for Beijing MTR Construction Administration, which is in charge of building the company's projects, said: "We have a safety and emergency command center that monitors the whole process from construction of the facilities to test runs."

The center came into operation in January.

A second monitoring center is designed to ensure that lines operate safely. This supplies information about passenger flows and other data to the government to help it reach decisions on the future development of the network.