Cast and crew members of The Wiggles administered CPR, while an off-duty nurse used a defibrillator three times to save the life of former band member Greg Page when he suffered a cardiac arrest on Friday night.

Page, 48, collapsed on stage and stopped breathing while performing at a bushfire relief concert at the Castle Hill RSL, north-west of Sydney, due to a serious cardiac arrest.

Original Yellow Wiggle Greg Page collapsed on stage at the end of a bushfire relief concert in Sydney.

Page, the Yellow Wiggle, subsequently underwent a medical procedure and is now recovering in hospital, with the group releasing a photo of the children's performer sitting up in a hospital bed smiling around midday on Saturday.

A short time earlier the group's manager Paul Field expressed his gratitude for the first responders who performed lifesaving CPR on Page.

"He was in such a serious way last night, he needed CPR ... he stopped breathing a number of times. It was quite dramatic," he told 7News outside Westmead Hospital.

"We had two of our cast and crew working on him. They used the defibrillator on him two or three times ... there was a nurse in the audience ... they saved his life," he said.

The 23-year-old off-duty nurse was in the audience when Page collapsed and immediately responded by using a public access defibrillator in the RSL club.

Footage from the concert shows Page, who suffers from a circulatory system disorder, singing and dancing on stage with the other original band members just moments before he collapses towards the end of the show.

The sold-out over-18s reunion show was being livestreamed at the time, with all proceeds going to the Australian Red Cross and WIRES following the devastating bushfires.

Greg Page, the original Yellow Wiggle, was taken to hospital after a medical incident. AP

"Thank you everybody," Page says, waving to the crowd and smiling.

"Thanks for coming to support all of those wonderful people doing all that great work for everyone."

As the crowd cheers, Page walks to the side of the stage and collapses.

Several people can be seen running across the stage and the curtain is partially pulled across to shield him from the audience.

Murray Cook, the original Red Wiggle, then returns to the stage to speak to the crowd.

"Guys I think we're going to end it there. Greg's not feeling real well. I think he's going to be OK but he's not feeling real well so I don't think we can go on with another song," he says.

The other band members do, however, return a short time later and perform the song Hot Potato.

"We're going to sing it for Greg and hope he gets better real quick," Blue Wiggle Anthony Field says.

Medical condition

Page has spoken publicly before about suffering from orthostatic intolerance, an often undiagnosed circulatory system disorder that affects blood flow.

In his memoir Now and Then: The Life-Changing Journey of the Original Yellow Wiggle, Page talks about how the illness forced him to leave The Wiggles in 2006, after 15 years of touring the world with his best friends. He returned to The Wiggles briefly in 2012, but retired again the same year.

Greg Page has spoken publicly before about suffering from orthostatic intolerance, an often undiagnosed circulatory system disorder that affects blood flow. Simon Alekna

People with orthostatic intolerance lack a nervous system that adequately moves the blood around their body, so that when they sit or stand for any length of time, blood instead pools in their pelvis or leg regions, causing them to faint.

For more than a decade, Page suffered embarrassing symptoms that made him worried others might think he was drunk. He often felt disoriented and vague, dizzy when standing upright for long periods and even slurred his words. He sometimes walked into walls and missed his mouth while eating dinner.

"I became almost a social recluse, incapable of communicating at any great level with anyone," he writes of how it affected him.

"It would exhaust me just to think, let alone talk or walk.

"I wanted to give more attention to this condition, to help people diagnose it and [deal with] the frustration that comes with being misdiagnosed."

The original Wiggles line-up of Page, Field, Cook and Jeff Fatt were performing on Friday night, the first of two planned fundraisers for the bushfire relief effort.

It was the first time they had appeared onstage together since 2016, when they performed an adults-only 25th-anniversary event as a fundraiser for returned services charity Soldier On.

In an updated statement on Saturday, The Wiggles confirmed their second fundraising show would still go ahead on Saturday night.

"Greg's main concern was that the show tonight should go on.⁣ Let’s do it for Greg whilst raising much needed funds."