Sir Elton John has moved tomorrow's Mt Smart Stadium show to Wednesday on doctor's orders.

The music legend was forced to cut last night's concert short, leaving the stage about two thirds of the way through, after contracting "walking pneumonia" and losing his voice.

A statement issued earlier today said that, as of this morning, the remaining shows, originally scheduled for Tuesday and Thursday would go on: "He is resting today, and doctors are confident he will recover."

A new statement, issued about 4pm, said the second gig would be delayed so John has an extra day of recovery on his current medication.

"I'm looking forward to seeing you on Wednesday and Thursday evenings at Mt Smart Stadium," he told his fans.

All Tuesday tickets remain valid for Wednesday. All concert details, including transport, remain the same.

The latest statement said Tuesday ticketholders unable to attend on Wednesday should contact Ticketmaster to request a refund. Limited tickets are still available for Thursday's show.

John, 72, broke down in tears last night when he realised he couldn't complete his set.

"I'm sorry, so very sorry," he told the Mt Smart crowd.

The superstar, who earlier needed medical assistance while on stage, had to be assisted from the stage after attempting to launch into Daniel, but having no voice left.

The song was number 16 in a 25-strong playlist. Herald concert reviewer Karl Puschmann said John's voice remained powerful during his early songs — until he spoke.

John later reached out to fans on social media saying he was "disappointed and deeply upset" that he couldn't complete his show.

Sir Elton's promoter has confirmed there won't be refunds for disappointed fans after the music legend's show was cut short.

Michael Chugg told Newstalk ZB's Heather du Plessis-Allan that the performance last night was just six songs short of a full short. 

He said that the Wednesday concert is definitely going ahead, and there will be options for customers to rearrange their flights. 

For those who feel shortchanged by the shortened concert on Sunday, Chugg says that as  the singer played over two hours, there won't be refunds offered.