An autograph manuscript of Mozart's Kyrie in C Major, smuggled out of Nazi Germany by its owners, has been consigned to a Sotheby's auction.

This is the most significant Mozart manuscript seen at auction in recent years

The manuscript, the most significant work from Mozart to have appeared for sale in more than a decade, is one of the highlights of the Music, Continental and Russian Books and Manuscripts auction on May 20 in London, starring with a £300,000-500,000 ($507,891-846,489) estimate.

Kyrie in C Major was composed in 1772, when the young Mozart was just 16 years old. However, having completed five pages, he abandoned the composition, leaving scholars clueless as to what the remainder might have sounded like.

It was then saved from the Nazi regime by a Jewish musician named Rudolph Gotz, who fled from Munich to South America.

"The family couldn't take obvious valuables or currency with them when they left so they took this. We don't know how much it cost but in the 1930s something like that didn't make a lot of money," commented Sotheby's specialist Simon Maguire.

"Ten years earlier there had been a whole auction of Mozart manuscripts that would be worth millions today, but half of them failed to sell."

With the cover removed to further conceal its identity, the work has been consigned by Mr Gotz's daughter, who would like to see it returned to Austria or Germany. It will star alongside the only known manuscript of Rachmaninov's Second Symphony, an incredibly important work.

Classical fans will also be able to bid on a previously lost manuscript by German composer Mendelssohn at Christie's on May 21. See the video below to hear the song, which nobody alive had heard until recently.