Heart-warming footage shows the moment a New York City subway car full of passengers bursted into song together.

The spontaneous sing-along came after a passenger in walked into the middle of the train playing the Backstreet Boy's hit song "I Want it That Way" on his speaker.

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Heart-warming footage shows the moment a New York City subway car full of passengers spontaneously bursts into song together.

The touching sing-along came after a passenger in walked into the middle of the train playing the Backstreet Boy's hit song 'I Want it That Way' on his speaker.

Others started to sing along and before long the entire carriage joined in.

The footage shared on Twitter by Joel Wertheimer, a civil rights attorney, has since been viewed more than 1.5 million times, with thousands of people also sharing the post.

Mr Wertheimer wrote on Sunday night: "Had a really tough week and tonight I was on the subway and some buy walks between train cars, shirtless, bumping a speaker.

"I wasn't in the mood for showtime particularly. But sometimes people and life surprises you and a little magic happens."

Read more: New York City has caught an alleged subway bandit who delayed more than 700 trains by pulling the emergency brake

Scores of people reacted to the footage, with one person saying the spontaneous moment is "part of what makes NYC special. Easy to hate it but also easy to love it".

One wrote: "Everybody from different places and we all get along. That's how we New Yorkers do."

"Seeing complete strangers, of all different races and backgrounds, bonding together in this fashion puts the biggest smile on my face," another person said.