The bunker was built to shelter people in the event of explosions, emissions of poisonous gas or nuclear radiation, the Xinhua news agency said.

It covered a total area of more than 90,000 square meters (968,400 square feet), with 15 passages nearly 4,000 meters (13,200 feet) in length linked to office towers and residential apartments, it said.

The bunker was connected to the city's subway system, allowing people to flee from one district to another, Xinhua said.

Xinhua cited an official with the Civil Defense Office as saying that water, power and ventilation systems in the bunker could provide shelter for up to 15 days.

In peacetime, parts of the bunker could be used as garages, warehouses or commercial facilities, the official said.

While terrorism was not mentioned as a reason for the project, the government has stepped up anti-terrorism efforts, last year establishing anti-terror and anti-riot police units equipped with everything from batons to helicopters.

It also set up an anti-terrorism police center in its restive Muslim region of Xinjiang which includes training grounds where cadets are schooled in the prevention of hijackings of trains, cars and planes.

Industrial accidents resulting in chemical leaks and accidents from the transportation of hazardous materials are also becoming more common throughout China.

Shanghai, in China's east, is the country's financial center with a population of around 17.8 million in a city area of about 5,155 square kilometers (2062 square miles).

The city will host the 2010 World Expo, which is expected to attract more than 70 million visitors.

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