Michelangelo's "Last Judgment", a Renaissance masterwork in the Vatican's Sistine Chapel that depicts the Second Coming of Jesus, is undergoing its first restoration in 30 years.

Experts will work over three months to remove decades of built-up particles that have obscured the colours of the artwork, the Vatican said in a press release.

"The new intervention... will allow the removal of these deposits and the consequent recovery of the chromatic and luministic quality desired by Michelangelo," it said.

The Sistine Chapel, famous as the site of the secret conclave where the world's Catholic cardinals vote to select new popes, sees millions of visitors each year as part of the Vatican Museums.

The chapel will remain open during the restoration. But the fresco itself, showing Jesus delivering his final judgment of humanity, will be covered by scaffolding.

Visitors will instead be able to see a high-definition reproduction of the artwork, the Vatican said.

The chapel is also home to many other frescoes, including Michelangelo's "The Creation of Adam" on its ceiling. Those will still be on display.