In the modern metropolis of Shanghai, construction has been completed on an underground bunker that can accommodate up to 200,000 people.

Its builders could have had the words of Chairman Mao in mind. At the height of the 1966-76 Cultural Revolution, he said: “Dig deep tunnels, store piles of grain. Prepare for war, prepare food for the people.”

The bunker in Shanghai was built to shelter people in case of explosions, emissions of poisonous gas or nuclear radiation. State-run media gave no clue as to the source of such possible attacks. Nor did it explain how a complex covering 90,000sq m (968,400sq ft), could have been constructed in total secrecy.

The report yesterday was the first word about it. The underground haven has 15 passages nearly 2.5 miles (4km) in length that link to office towers and residential apartments. It is also connected to the subway system, enabling people to flee from one district to another. It was not clear where the rest of the city’s 17.78 million residents would take refuge.

Water, power and ventilation systems can support the bunker’s population for between seven and fifteen days. In times of peace, some parts can be used as garages, warehouses or commercial facilities.

Officials stopped short of revealing the exact location of the bunker in the bowels of a city renowned for its futuristic buildings and role as the financial heart of China.

It was already known that Shanghai had at least one underground bunker, a small concrete facility built for Mao in case of need during his visits to the city.

The bunker cannot compete in scale with the estimated 19 miles of air-raid shelters dug underneath Beijing in the 1960s and 1970s. The capital’s “Underground Great Wall” featured a munitions warehouse, hospital, theatre and library and was believed to have a capacity of up to 300,000. It has now been transformed into a tourist complex with bars and dance halls.

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