What is the standard English phrase for releasing many unexpected problems at once, inspired by Pandora's myth?

The standard English phrase is “opening Pandora’s box.”

The expression describes an action that creates or releases many unforeseen problems, complications, or harmful consequences. It comes from the myth in which Pandora opens a sealed container and troubles escape into the human world.

The idiom is usually used figuratively rather than literally. A person may say that investigating one issue “opened Pandora’s box” when the investigation reveals a much larger and more difficult set of problems. The phrase commonly carries a warning that an apparently small action can have wide effects.

The expression’s wording reflects later translation history. Hesiod’s original container was a pithos, a large jar, but Renaissance Latin translation helped turn the vessel into a box in European languages. “Opening Pandora’s box” therefore combines an ancient Greek story with a later linguistic development.