Australian and international entertainers, from the past and present, have paid tribute to John Farnham in a concert raising funds for head and neck cancer.

Thousands filled Melbourne's Rod Laver Arena for the sold-out show, with many more watching around the country as the concert was beamed to select cinemas live.

The concert marks the beginning of the Lend Your Voice campaign to raise $1 million for Head and Neck Cancer Australia over the next year, with Farnham partnering with the organisation that helped support him through his own journey with cancer.

Farnham underwent a marathon surgery to remove a cancerous tumour in his mouth in 2022, and was given the all clear by doctors the following year.

Richard Wilkins served as MC for the evening, introducing what he described as a "cavalcade of supreme talent".

Wilkins said Farnham had sold out 94 shows at Rod Laver Arena over the years, the most of any performer ever.

"So I guess tonight makes it 95, an unbelievable 95," he said.

Farnham himself was not able to attend the concert, with his family confirming that the 77-year-old's health had declined recently, leaving him unable to take the stage at Rod Laver.

"John's health has deteriorated in recent months. He now requires continuous oxygen support and uses a wheelchair for mobility," the Farnham family said in a statement.

"It has also become necessary for John to receive 24-hour nursing care at home, ensuring trained support is always available when he needs it."

But Farnham was still a presence in the arena, with footage of his former sell-out performances beamed on screens as the musical numbers began.

Australian and international stars pay tribute

The concert began firing on all cylinders, introducing an all-star opening line-up of Jessica Mauboy, John Stevens, Jack Jones, Mahalia Barnes and Human Nature to sing a medley of Farnham songs, including the title track to 1988's Age of Reason, 1986's Reasons and 1996's Have a Little Faith (In Us).

The Farnham clan was still represented onstage, with John's son Rob Farnham singing Love To Shine from the album Whispering Jack.

He thanked those in attendance, following his performance, and said his dad would be touched to see the turnout.

"We all know he's a little bit too humble for his own good sometimes," he said.

"To see all these people here would just absolutely warm his heart."

The concert also paid tribute to Farnham's theatre career, including his 1992 turn in the title role of Jesus Christ Superstar.

His then co-stars Kate Ceberano and Jon Stevens performed Everything's Alright from the hit musical before sharing a hug onstage.

The crowd couldn't contain itself as Wilkins announced the next guest, saying he had flown in from Nashville, Tennessee to be at the show.

"Tonight, he is back home and he's all ours," Wilkins said as the crowd roared and Keith Urban made his way onstage, stunning the audience with his rendition of 1990's Burn For You.

The international guests kept coming, with Celine Dion beaming in from a stage in Paris to perform, apologising to fans in attendance for a scheduling conflict.

"John, you've always been such a deep inspiration to me; I always loved to hear you sing," Dion said.

"The way you sang one song in particular is one of my very, very favourite performances ever."

Dion said she sang this song as a duet with Farnham during her last visit to Melbourne and launched into You're The Voice, bringing the crowd at Rod Laver Arena to its feet.

The duets continued as Jimmy Barnes came onstage to perform When Something Is Wrong with My Baby, a 1991 track Farnham and he collaborated on, with Barnes's daughter Mahalia Barnes filling in onstage for John.

Actor Hugh Jackman also performed via simulcast, sharing stories of sneaking in to see John Farnham do his sound check at the Perth entertainment centre as a youth, before singing the country-flavoured track Talk of The Town.

"I've been a fan of yours as long as I can remember. I have seen you at least 30 times live, and I would say you are one of the greatest I have ever seen onstage," Jackman said.

"The person I am onstage, the entertainer I am, is largely because of you."

Fans flock from around the nation for Farnsy

Leanne, who travelled to Melbourne from Tasmania for the concert, said she had plenty of tissues ready for an emotional evening.

Proudly wearing an autographed T-shirt, she said her whole house was filled with Farnham memorabilia, in tribute to a man who helped her during a health scare of her own.

"Years back I was in a coma, and my family said that the only thing I actually responded to the whole time was John Farnham music, so I'd kick my leg and tip my hand," Leanne said.

Leanne said she had heard the news that Farnham would not be able to attend, and was hoping for the best.

"I think I knew deep down it was coming, but it's just been devastating and all we can do is pray that he's going to be OK," she said.

"He is our voice, he's always been my voice and he'll never walk alone."

For some, just attending the concert wasn't enough to show their affection for Farnham.

Geelong residents Rob, Angie and Jo went the extra mile to unleash their best mullets and whip out the double denim.

For Angie, the trip to Rod Laver Arena was particularly special, as it was where she saw Farnham perform for the very first time.

"First ever concert when I was 13 years old was right here, 36 years ago, and I saw John Farnham," she said.

"I'm going to get teary already, it's already started … I plan to cry a lot."

Angie owns a karaoke bar in Geelong, where the final song of the night is always You're The Voice, and she said the place was full of mullets and denim last night in preparation.

"All his songs, I get goosebumps now just thinking about it, his music has changed the hearts and minds and lives of people all over the world, why wouldn't we come and celebrate him?" Jo said.

Fans Kate and Jason travelled from Brisbane for the show, with Kate saying she has loved Farnham "so badly" ever since seeing him perform in Jesus Christ Superstar.

She said the fundraising effort behind the concert carried an even more personal meaning.

"My sister's had treatment for 17 years for head and neck cancer, and the work that field does is tremendous," she said.

"When I found out that the proceeds were going towards that, it just made it even sweeter."

Focus on raising awareness

Head and Neck Cancer chief executive Nadia Rosin said the organisation was incredibly grateful to Farnham and his family for shining a spotlight on the disease.

"They're cancers that affect the very essence of a person, it's obviously affected John's voice," she said.

Spot check-up sites were set up at Rod Laver Arena, with concertgoers able to have their mouths swabbed and checked for signs of cancer.

Ms Rosin said a similar initiative at a John Farnham concert earlier this year in Melbourne to raise awareness about cancer was highly successful.

"We had dentists checking people for oral cancer," she said.

"We had about 300 people through in the space of an hour, and six of those people were referred for further investigation because of something suspicious in their mouth."

Ms Rosin said about 14 Australians were diagnosed with head and neck cancer every day, making the concert a crucial opportunity to raise awareness.

"If everyone can walk away thinking about oral cancer and head and neck cancer and having that on their radar, then our job will be done," she said.