Wiggles lead singer Greg Page has collapsed on stage during a reunion concert for bushfire relief.

The group were moments away from performing their final song, Hot Potato, at the concert at Castle Hill RSL in Sydney when Yellow Wiggle Page collapsed.

Shocked concertgoers were left stunned as the concert was stopped, with paramedics rushing to Page's side to perform CPR.

A while later, the rest of the band returned and told the 800-strong crowd their singer 'needed medical attention'.

Page suffers with orthostatic intolerance, a circulatory system disorder which causes blood to pool in his legs - making him faint.

The Wiggles' lead singer Greg Page (pictured) is seen at a concert in Miami Beach in 2012. He collapsed on stage in Sydney on Friday night

In a video from the packed-out concert on Friday night, Greg Page (right, in yellow) can be seen desperately grappling for something to hold on to as he collapsed by the side of stage

Video from Friday night shows Greg Page (right, in yellow) falling to the floor as he collapsed, sparking an urgent call to paramedics

Behind Red Wiggle Murray Cook, the sleeve of Greg Page's iconic yellow top (right) can be seen after he suffered the terrifying collapse

What is orthostatic intolerance - and how serious is it? Orthostatic intolerance (OI) is when a person's body struggles to pump enough blood When a person stands upright for a prolonged period, 750ml of blood flows downward For those with OI, their body struggles to compensate for this This means there is a lack of blood in other areas of the body, causing them to faint Orthostatic means 'upright' Advertisement

He is in a serious but stable condition at Westmead Hospital.

It comes after his doctor previously warned the illness means he would need to 'be careful with the rigors' of performing.

'Thank you everybody,' he is seen saying as he waved to the crowd and smiled.

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

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

People are then seen rushing to his aid as the stage curtain draws in to hide him from the audience.

A short while later, the original Red Wiggle, Murray Cook, returned and said Greg 'was not feeling real well'.

Blue Wiggle Anthony Field shared a photo of the group backstage, writing: 'We are all in shock, please get better mate, I'm praying for you'

Wiggles characters are seen rushing to the side of the stage on Friday (pictured) shortly after Page collapsed

The Wiggles' Greg Page (pictured, in yellow) is seen on stage just minutes before his dramatic collapse in Sydney on Friday

'Guys I think we're going to end it there,' he said.

'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.'

The other band members later return to the stage to sing fan favourite Hot Potato, dedicating it to their friend.

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

At 11.20pm, the band released a statement on Twitter saying Page was in hospital.

A concertgoer shared a photo of the ambulance which arrived to treat Page (pictured) after his collapse on stage

Greg Page (pictured, left) waves to the excited crowds in Sydney on Friday night just minutes before he dramatically collapsed and was rushed to hospital

The original Wiggles line-up reunited for the sold-out bushfire relief concert in Sydney. Here they are pictured in 2012, the last time they performed together

'At the end of the show this evening there was a medical incident off stage involving Greg Page,' it said.

'Medics were called immediately and he was taken to hospital where he is receiving treatment. We will provide more information as it comes to hand.'

A second update four hours later said: 'Our friend Greg Page suffered a cardiac arrest at the end of the bushfire relief performance and was taken to hospital.

'He has had a procedure and is now recovering in hospital. We appreciate your kind messages and concern.'

A NSW Ambulance spokesperson said paramedics were called at around 10pm on Friday night to the Castle Hill RSL after reports a man had gone into cardiac arrest.

They said a 48-year-old male who had collapsed was being treated in hospital in a serious but stable condition.

He was breathing when paramedics arrived, but crews performed CPR.

In autobiography Page wrote about his struggle with orthostatic intolerance, which forced him to quit the Wiggles in 2006.

Those who suffer with the condition, which is often undiagnosed for years, have a nervous system which struggles to move enough blood around the body.

The frightening circulatory condition caused Page (pictured, back) to leave the Wiggles back in 2006

The Wiggles in numbers First forming in 1991, the Wiggles have been performing for nearly 30 years They have released 53 studio albums They've earned approximately $240m More than 30 million albums and DVDs have been sold Advertisement

This means that when they stand for a long period of time, the blood can pool in their legs and cause them to faint.

'Just knowing that what I had had a name, and it wasn't terminal, and it could be treated was wonderful. I feel like I'm getting a second chance,' he wrote.

His physician, Dr. Susan Corcoran, told People: 'Simple measures have been effective in helping his condition, but he'll need to be careful with the rigors of the tour.'

In his book, Page discussed the painful decision to quit the band to focus on his health.

His condition saw him suffer 'bouts of acute dizziness' that left him 'unable to stand, speak or think without great difficulty'.

The singer also admitted that the struggle to get diagnosed left him suffering from depression.

On Friday night, concerned fans immediately took to social media to express their fears for the beloved star.

The original Wiggles - Greg, Anthony, Murray, and Jeff - reunited for their first show together since 2012 (pictured)

'Greg from the Wiggles collapsed during the charity concert and was sent to the hospital in an ambulance and I’m literally crying over it,' one fan wrote.

'Please I love him he was part of my childhood. I really hope he’s okay.'

'All my love to Greg and his family,' another wrote.

'He was truly a champion tonight, powering through for those in need. We're all hoping and praying for his recovery.'

Page has two children, Madison and Blaine, with his ex-wife Michelle Charlton.

He married his second wife, Vanessa, in 2011 and had two more children.

A keen Elvis Presley fans, he has the fourth largest collection of Elvis memorabilia in the world.

Current Wiggles Simon Pryce, Emma Watkins, Lachlan Gillespie and Anthony Field (left to right) are seen in November 2019 in Sydney

The original Wiggles, Murray Cook, Jeff Fatt and Anthony Field joined Page at the concert, marking the first time the original line-up performed together since 2012.

Currently, only one of the original line-up, Blue Wiggle Field, is in the official band.

He is joined by Simon Pryce, as well as divorced couple Lachlan Gillespie and Emma Watkins.

Discussing her split from her husband, and fellow Wiggles performer, after two years of marriage, Ms Watkins said they are still 'best friends'.

'We're basically back to being best friends again which is nice,' she told the Project in December.

She said their relationship has been 'so good' despite working closely together and the fact that she now dates Wiggles musician Oliver Brian.

Wiggles star Emma Watkins (pictured, left) said her relationship with her estranged husband Lachlan Gillespie (right) has developed to the point they are once again 'best friends'

'Lachy' and Yellow Wiggle Ms Watkins left their fans stunned when they announced the end of their two-year marriage back in August 2018.

They pair joined the Wiggles in 2013, and began dating just weeks later.

But they kept their romance secret for the next two years as they performed all around the world.

In March 2015, the couple went public with their relationship and became engaged just two months later.