Ms Emily Zamourka, 52, was singing in a Los Angeles subway station next to a pushcart with her belongings when a police officer recorded her rendition of Giacomo Puccini's O Mio Babbino Caro and uploaded the video on Twitter.
"Four million people call LA home. Four million stories. Four million voices... Sometimes you just have to stop and listen to one, to hear something beautiful," said the tweet.
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