Imagethief read with interest that Shanghai has completed a "vast bunker" to be used in case of explosions, emissions of  poisonous gas or nuclear radiation:
China's largest metropolis has completed building a vast bunker in case of explosions, emissions of poisonous gas or nuclear radiation, [a] news report said Sunday.

The complex covers 90,000 square meters and can accomodate 200,000 people, according to the Shanghai Morning Post.

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.

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, the report said.

The article did not mention the exact location of the bunker.
First, Imagethief is shocked and dismayed that Beijing, the national capital, has not announced a similar bunker, although many local apartment buildings thoughtfully incorporate bunker features into their parking garages (most of which are, unfortunately, desperately short of the amenities that might make an extended stay tolerable).

Second, Imagethief also notes that the bunker system, while genuinely colossal, has capacity for only 1% of Shanghai's population. In fact, even that seems optimistic, given that the bunker has 90,000 square meters for 200,000 people, or 0.45 square meters per person. Imagethief suggests you try occupying a space of 0.45 square meters for seven to fifteen days, and then tell him how it works out. Imagethief can visualize this situation by imagining the same ratio applied to his apartment, which would yield an occupancy of 288 people. That is significantly more than the fifteen which I once had over for a party, and which felt pretty crowded. Faced with that kind of crowding, you might, with some justification, choose the radiation instead. (Charitably, the math might have been blown in the translation.)

A bunker connected to office towers, residential apartments and the subway system could be expected to fill rapidly with businesspeople, expats and cadres. That's fine, but it seems likely that Shanghai civilization as we know it would likely grind to a halt without taxi drivers, ahyis and migrant laborers. Even assuming the cream of Shanghai survived the rough overcrowding.

Keep digging.