all of a sudden

All of a sudden the fireworks warehouse exploded.
突然、花火倉庫が爆発した。

チャット爺に訊いてみました。

“All at once” and “all of a sudden” are phrases that are often used interchangeably in casual conversation, but they can carry slightly different nuances or emphases in their meanings.

All at Once:

This phrase generally means that multiple things are happening simultaneously or that something is being done completely and in totality. It can indicate a situation where several events or actions occur at the same time, or it can refer to doing something in one single effort or moment, rather than in stages.
Example: “All at once, the lights went out, the music stopped, and a hush fell over the crowd.”

All of a Sudden:

This phrase is used to describe something happening unexpectedly and quickly, emphasizing the suddenness and the surprise element of the event. It doesn’t necessarily imply that multiple things are happening at the same time, but rather that something changed or happened very quickly and without warning.
Example: “All of a sudden, it started to rain heavily, disrupting the outdoor event.”

In summary, while both phrases can sometimes be used interchangeably in the context of something happening unexpectedly, “all at once” often implies multiple things occurring simultaneously or something being done completely in one effort, whereas “all of a sudden” emphasizes the abruptness and unexpected nature of a single event or change.