Singer-songwriter Neil Diamond performs on stage during the 84th Rockefeller Center Christmas Tree Lighting at Rockefeller Center on November 30, 2016 in New York City.

World-renowned singer, songwriter and performer Neil Diamond has announced his retirement from touring after being diagnosed with Parkinson's disease.

Acting on medical advice, Diamond cancelled the upcoming Australia and New Zealand legs of his 50th Anniversary tour, which were set to commence in March.

Parkinson's disease is a long-term degenerative disorder which affects the motor systems. It is characterized by shaking, rigidity and difficulty with walking.

The disease makes it difficult for the singer to travel and perform on a large scale, but he said in a statement that he expects to continue writing, recording and developing new projects

"It is with great reluctance and disappointment that I announce my retirement from concert touring. I have been so honoured to bring my shows to the public for the past 50 years," Diamond said in an announcement on his website. "My sincerest apologies to everyone who purchased tickets and were planning to come to the upcoming shows."

The singer added: "My thanks goes out to my loyal and devoted audiences around the world. You will always have my appreciation for your support and encouragement. This ride has been 'so good, so good, so good' thanks to you."

The Australia and New Zealand leg of the tour would have been the third leg of the 50th Anniversary route with Diamond selling out shows in the U.S. and Europe throughout 2017.

Ticket holders for the cancelled shows have been advised that they will be automatically refunded in full if they purchased by credit or debit card. Those who purchased tickets with cash of EFTPOS will be contacted to arrange a refund.

Diamond is due to celebrate his 77th birthday on Jan. 24.