[ycui1986]

These bunkers has multiple rooms. It is not uncommon to have 8 people living in one room, and a large bunker site can have 20+ rooms. A bunker site can have living area similar to a 20 room motel, underneath a much bigger building on top (at least when they are inside the city).

Since these bunkers were built, they were build for war, some of them have very thick gas tight door to complete seal the environment from outside.

[sbenitoj]

Citation?

[seanmcdirmid]

Think about how many apartment buildings are in Beijing. All of these have basements, each basement level has multiple rooms, and most apartment buildings have multiple levels of basement. A million people easily could be sheltered under that context.