while looking on in blank amazement; before one knows it
Describes a situation where events unfold so quickly or unexpectedly that the observer can only watch in stunned disbelief, often with a sense of helplessness or surprise. Used adverbially.
See also: あれよあれよ
Before anyone knew it, he had risen all the way to company president.
あれよあれよという内に、火は家全体に広がった。
While we looked on in shock, the fire spread throughout the entire house.