Jimmy Barnes and Keith Urban both say AC/DC's Malcolm Young is the best rhythm guitarist they've ever seen, as tributes flow in for the Australian music icon, who has died aged 64.

Young, who was known for the powerhouse riffs and rhythm guitar that propelled the Sydney group to world superstardom, died on Saturday after a three-year battle with dementia.

Australian rocker Barnes said Young was "the greatest rhythm guitar player ever" and extended his condolences to his brother and fellow AC/DC star Angus Young.

"What a sad day for music," Barnes posted on Twitter.

Australian country music star Urban said he was "devastated" by Young's death.

"For me personally, the GREATEST rhythm guitarist of ALL TIME," Urban tweeted.

"Thank you Malcolm for all of the spit and fire, passion, ferocity, gravitas, and for the eternal inspiration."

Eddie Van Halen is among a large cohort of international rock greats who have also paid homage to Young online.

"Malcolm Young was my friend and the heart and soul of AC/DC," Van Halen said.

"I had some of the best times of my life with him on our 1984 European tour. He will be missed and my deepest condolences to his family, bandmates and friends.

Others who remembered Young are Black Sabbath's Ozzy Osbourne, Motley Crue co-founder Nikki Sixx, Rage Against the Machine axeman Tom Morello and KISS frontman Paul Stanley.

Young was replaced by his nephew Stevie for AC/DC's last tour promoting the 2014 album Rock Or Bust, after dementia forced him into retirement.

He died peacefully on Saturday with his family by his bedside, a statement from the family said.

Formed in Sydney in 1973 by Malcolm and Angus, AC/DC built a loyal Australian fan base on the back of relentless touring and albums such as Powerage and Dirty Deeds Done Dirt Cheap.

The band survived the 1980 death of frontman Bon Scott, returning with the classic Back In Black, which remains the second-biggest selling album of all-time with an estimated 50 million copies sold worldwide.

Young last featured on the band's Black Ice tour, which ran from 2008 to 2010 and is survived by his wife, Linda, and their children Ross and Cara.

Angus shared the sad news on the AC/DC Facebook.

"As his brother it is hard to express in words what he has meant to me during my life, the bond we had was unique and very special," he posted.

"He leaves behind an enormous legacy that will live on forever.

"Malcolm, job well done."

Malcolm and Angus' older brother George, who paved the way for his siblings with legendary 1960s group The Easybeats before finding further success as a songwriter and producer with ex-bandmate Harry Vanda, died last month aged 70.