It is not commonly used elsewhere (don't know about NZ), but in South Africa, we do use it ... we were packed like sardines. We have the Sardine Run happening next to our coast every year... so I suspect it brings sardines into our consciousness more than most.

I'm not native but anyone can say that "the subway" cannot be "packed" -- instead "People should be the subject: «--- People in the subway are packed like sardines.» Moreover I don't think that this is a properly said "idiomatic expression", just a figure of speech -- like «--- Your eyes are blue as the sky» -- and you can express the same concept in many variants. Creative writing infact is about challenging the boundaries of language, not sticking on idiomatic expressions, right? "Packed like sardines" is a totally legitimate expression but maybe "Crammed like sardines" or "Squashed like sardines" are even more coloured (actually I found «Squashed like sardines» on the web). Bye ;

Australian English still uses the following, Its packed like a tin of sardines in here We are squashed in like sardines The room/train is chock a block full (of people), also shortened to "It's chocka in here" It's stuffed full It's packed to the rafters All these refer to crowded buildings and maybe trains except the last one. Rafters are in buildings. I think crowded words are a bit cultural. In Japanese, I think it is konde imasu. 混んでいます

I've heard "crammed in like sardines." Example: We're crammed in like sardines. But I'm sure it varies by region. But in my opinion it's not commonly used. I would say something like: "it's really crowded," "there's a lot of people here," "it's packed," ect. Hope that helps!