expression, adverb
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.
観光客が雲霞のごとく押し寄せた。
Tourists came flooding in like a swarm.
戦場に兵士たちが雲霞のごとく集まった。
Soldiers gathered on the battlefield in droves.
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.