in swarms; in droves; in great numbers
Describes a large number of people, animals, or things moving or gathering together, often with a sense of overwhelming multitude. Used adverbially.
Tourists came flooding in like a swarm.
Soldiers gathered on the battlefield in droves.
群れをなして means 'in flocks/groups' and is more concrete about forming groups. 雲霞のごとく is more figurative and grand in scale.
Standard kanji spelling with hiragana ごとく.
Variant using the kanji 如 for ごとく; slightly more formal or literary.
From 雲霞 (clouds and haze/mist) + の + ごとく (like, as if). Literally 'like clouds and haze', evoking an image of something vast, dense, and spreading.