A new piece of music believed to be by the Polish composer Frederic Chopin has been discovered nearly 200 years after it was written.

The unknown waltz was unearthed in the vault of the Morgan Library and Museum in New York.

The rare manuscript - dated between 1830 and 1835 - was discovered by curator Robinson McClellan while he was cataloguing new collections.

He then worked with a leading Chopin expert to authenticate the score.

It is not signed by Chopin, but the handwriting includes his distinctive bass clef.

The waltz has minor errors in rhythm and notation but Mr McClellan said he is sure that Chopin is behind it.

"What we're most certain about is it is written in the hand of Chopin, paper that he wrote on himself in his own hand," he told BBC's Newshour.

"What's not entirely sure is that it's music that he composed.

"I feel about 98% sure, and many people who have heard it already feel in their gut this sounds like Chopin."

He continued: "There are atypical aspects of the music, the kind of stormy opening is a little surprising but not entirely out of character.

"And then the melody really to me is where you feel that Chopin quality."

Superstar pianist Lang Lang has recorded the waltz for the New York Times, which broke the story.

Chopin, who wrote mostly piano solos, died aged 39 in France in 1849.

He was hounded by hallucinations during his relatively short life and probably had epilepsy, Spanish researchers believe.