Sir Elton John has said he is "deeply upset and sorry" for cutting short a concert after being diagnosed with walking pneumonia in New Zealand. John was performing at Auckland's Mount Smart Stadium on Sunday when he lost his voice and broke down in tears on stage. Posting on Instagram after the show, the star said: "I want to thank everyone who attended tonight's gig in Auckland. "I played and sang my heart out, until my voice could sing no more. I'm disappointed, deeply upset and sorry. I gave it all I had. "I was diagnosed with walking pneumonia earlier today, but I was determined to give you the best show humanly possible." What is walking pneumonia? According to the American Lung Association, walking pneumonia is a "non-medical term for a mild case of pneumonia". It can be caused by bacteria or viruses; the medical term "atypical pneumonia" - introduced in the 1930s - is given to any pneumonia not caused by one of the pathogens most commonly associated with the disease. Symptoms include a cough, fever, chest pain, mild chills, and a headache, and are similar to that of a bad cold, though there are few physical signs in general. View this post on Instagram I want to thank everyone who attended tonight’s gig in Auckland. I was diagnosed with walking pneumonia earlier today, but I was determined to give you the best show humanly possible. I played and sang my heart out, until my voice could sing no more. I’m disappointed, deeply upset and sorry. I gave it all I had. Thank-you so much for your extraordinary support and all the love you showed me during tonight’s performance. I am eternally grateful. Love, Elton xx 📷 @bengibsonphoto A post shared by Elton John (@eltonjohn) on Feb 16, 2020 at 1:30am PST Symptoms are usually mild enough for a sufferer to be able to continue their daily activities, and it is known "walking pneumonia" because one can often still be up and about. The patient usually looks better than the symptoms suggest. The disease is diagnosed through chest X-rays, which can show signs of an infection before physical evidence of atypical pneumonia are observable at all Will Elton John recover? Walking pneumonia is not usually as severe as other types of pneumonia and does not require bed rest or hospitalisation. In footage shared by fans on social media, Sir Elton was seen crying as he was escorted from the stage while thousands of concert-goers gave him a standing ovation. According to one fan on social media, Sir Elton had told the audience earlier in the show: "My voice has completely gone, I'm so sorry." He was tended to by a medic for around five minutes and continued to play before he was forced to stop completely. Sir Elton is due to play two further concerts in Auckland this week. He has been cleared to perform the remaining two shows, but the second show has moved to 19 February to allow for extra rest. His current tour, which began in 2018 and consists of more than 300 concerts worldwide, is intended to be his last, after the singer said he wanted to spend more time with his husband, David Furnish, and their two young sons. The performance in Auckland comes less than a week after Sir Elton and his writing partner Bernie Taupin won an Oscar for Best Original Song for the track '(I'm Gonna) Love Me Again', composed for biopic Rocketman.