The ones I saw in Japan had holes, I think it's the Chinese plugs that don't.
China has historically used a NEMA like plug, without holes for 220V 50Hz
It causes some interesting problems for US tourists.
Also, Chinese plugs of that type are not polarised, both pins are the same width and you can't always inserts a polarised US plug
They are phasing them out in favour of a plug very similar to the Australian/NZ one.
Note the pin layout is different to the Aussi/NZ setup i.e. it's ground at the top, like the UK/IRL
China 10A
China 16A
Comes in 10A and 16A versions
It seems they're phasing out the 2-blade plugs.
You will also encounter US NEMA or CEE 7/16 (Europlug) 2-pin plugs in China for Class II appliances.
and, in older installations you can encounter either BS546 (old british round pin plugs) or schuko.
BS1363 and modern Schuko can be found in some buildings too!
Also, they have unfused plugs which fit BS1363 sockets. These are designed for use on radial circuits, not UK rings.
However, they're a potentially serious fire hazard if connected to a UK ring circuit should they find their way to the UK.