A nurse who has been a fan of the Wiggles since she was a child has "saved the life" of founding member Greg Page after he suffered a heart attack during the group's bushfire relief concert in Sydney.

Key points: Page was performing a reunion show with his original Wiggles bandmates when he suffered a heart attack

Page was performing a reunion show with his original Wiggles bandmates when he suffered a heart attack He received first aid on-site by a nurse in the audience as well as two Wiggles crew members, before undergoing a procedure at Westmead Hospital

He received first aid on-site by a nurse in the audience as well as two Wiggles crew members, before undergoing a procedure at Westmead Hospital Page first retired from the Wiggles in 2006 due to orthostatic intolerance, which causes fatigue and blackouts

Former yellow Wiggle Page required CPR and a defibrillator after he had a heart attack and went into cardiac arrest as he left the stage at the end of the show.

He could be seen falling to the ground as he walked off stage at a Sydney reunion concert for bushfire aid on Friday night.

Nurse Grace Jones performed CPR on Page with the help of Wiggles drummer Steve Pace and staff member Kimmy Antonelli.

She then used a defibrillator supplied on-site at the Castle Hill RSL, where the incident occurred in front of a crowd of hundreds along with thousands more watching via live stream.

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"I took charge," Ms Jones said on Saturday morning. "I didn't mean to, but I did.

"I think I was the only one there who had any first aid training, so I just started to do what I do at work."

Chief Inspector at NSW Ambulance Brian Parsell said the quick response "saved Greg's life".

"When I was on stage and Greg was stabilised I asked who the person who used the defib was and Grace anxiously stepped forward," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 3 seconds 1 m 3 s Chief Inspector at NSW Ambulance Brian Parsell said the bravery and courage of nurse Grace Jones saved Page's life.

"I told her she needed to be congratulated because she had saved the man's life.

"She did an extraordinary job and it was only through her efforts and those who also performed CPR, that Greg is alive."

Page was performing with original Wiggles bandmates Field, Murray Cook and Jeff Fatt, with all proceeds from the show and livestream going towards the Red Cross Appeal and WIRES.

Wiggles members look where Greg Page collapsed to the side of the stage during their bushfire relief concert at Castle Hill RSL. ( Supplied: Epicentre.tv )

After a brief moment of confusion, Cook came back out to announce Page's condition.

"Greg's not feeling real well. I think he's going to be OK. He's not feeling real well," Cook told the live audience.

"He's going to be alright. We've got some medical attention."

An encore performance of Hot Potato was carried out without Page.

Mr Parsell said Page suffered a coronary occlusion, a blockage of one of the major blood vessels to the heart.

"He has had a heart attack which then led to a cardiac arrest," he said.

"He had been on stage for an hour, and you can imagine having been to a concert with my own children, it is an energetic concert.

Greg Page performing on stage at the Castle Hill RSL for bushfire relief. ( Supplied: Epicentre.tv )

"We performed an ECG and that identified that he had a blockage of one of the major primary vessels. We transmitted that ECG through to Westmead Hospital.

"We had the cardiology team already on the way in, out of bed and coming into the hospital so that we could reopen that blocked vessel."

He said Page was likely to make a full recovery.

"The timeline, from the time he collapsed and the time that vessel was reopened is very short," he said.

"So chances are he will make a fantastic recovery."

When asked if she had a message for Page, Ms Jones said: "I hope your chest is not too sore."

"I've been a Wiggles fan since I was five or six," she said.

"I didn't go to the concert expecting to do that, so it all feels a bit surreal.

"I do stuff like that every day at work but I have never had to do it with that equipment."

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Mr Parsell credited Ms Jones for her "courage" in stepping forward.

"Of all the people that were in the crowd, for Grace to come forward and offer her services to help and have the courage to use a defibrillator is an extraordinary story of survival, and we should be very thankful," he said.

Second show to go on tonight with Page's blessing

The 18+ concert on Friday night was the first of two planned with the original Wiggles line-up, with another scheduled for tonight.

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On Twitter, The Wiggles confirmed tonight's show would go on, with a substitute yellow Wiggle, with Page's blessing.

Donations for bushfire relief are approaching the $200 million mark from major companies and celebrities, but it is unknown yet how much the Wiggles fundraiser added to that tally.

Before walking off stage, Page farewelled the audience: "Thanks for coming to support all those wonderful people doing all that great work for everyone."

'He said to me: 'Did I finish the show?'

Wiggles manager Paul Field told ABC News he was able to visit Page at 3:00am in hospital.

"He was very groggy obviously," Field said.

"He couldn't remember anything about how it happened.

"Being a performer, he said, 'Did I finish the show?'

"I said, 'Yes mate, you finished the show.'"

Field was emotional while talking about last night's emergency.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 12 seconds 2 m 12 s Wiggles' manager breaks down describing Greg collapsing

"It was an awful experience for him and all those around him," he said.

"His mum and dad were there. It was quite traumatic to witness. But he was lucky to have those people who jumped in and did CPR.

"It was very touch-and-go and those people who did CPR on him saved his life."

Field said Page was likely to be in hospital for "some days".

He added Page was "adamant" Saturday night's scheduled show should go ahead.

"He said, 'so many more people are doing it tough'."

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Messages of goodwill to Page

Following the news, fans flooded The Wiggles' social media pages with messages of goodwill.

"Someone needs to tell me Greg Page is okay [because] I think I speak for all Australians when we say this is NOT how we are starting 2020," Liz Saunders wrote on Twitter.

Others expressed their sadness that Page suffered ill health while performing for charity.

"Greg and all the Wiggles are just so awesome and we were thrilled at the announcement of this bushfire relief gig," Janine Shearer said on Facebook.

Founding Wiggles member Greg Page (far right) collapses on stage at the Castle Hill RSL. ( Supplied: Epicentre.tv )

"The news of Greg's collapse is just devastating … sending massive positive healing vibes to our favourite yellow Wiggle of all time."

Page formed The Wiggles with Field, Cook and Fatt in 1991.

He retired due to illness in 2006 and was diagnosed with orthostatic intolerance, which causes fatigue and blackouts.

But he returned to his role as the Yellow Wiggle in early 2012.

Page, Cook, and Fatt retired together later that year, paving the way for the current iteration of Wiggles — Field, Emma Watkins, Lachlan Gillespie and Simon Pryce.