忽如一夜春风来

From Cen Shen's (岑参) Tang poem 《白雪歌送武判官归京》 (Farewell to Magistrate Wu in Snow): 忽如一夜春风来，千树万树梨花开 - 'As if a spring wind had come in a single night, ten thousand pear trees burst into bloom.' Originally describing snowdrifts on northern branches that looked like pear blossoms. Today almost always figurative, a social or technological phenomenon that appears everywhere overnight.

Very common in feature reporting on trends (tech, fashion, culture). Often completed with 千树万树梨花开 for a full echo of the original, or with a paraphrased version of what has 'bloomed' everywhere.