Music royalty Malcolm Young, the Australian guitarist and AC/DC co-founder, has died aged 64.

Known for the powerhouse riffs and rhythm guitar that propelled the Sydney group to superstardom, Young had been suffering from dementia for at least the past three years.

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

"With enormous dedication and commitment he was the driving force behind the band," AC/DC said on its website. "As a guitarist, songwriter and visionary he was a perfectionist and a unique man. He always stuck to his guns and did and said exactly what he wanted."

Younger brother Angus said the pair were close until the end.

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

Malcolm was replaced by nephew Stevie for the band's last tour promoting the 2014 album Rock Or Bust. He wanted the band to continue the tour.

"Mal always wanted the music to go on," singer Brian Johnson told Rolling Stone in 2014. "And I'm not going to say no."

According to Angus Young, Malcolm started battling symptoms of dementia before they made their 2008 album Black Ice, but he was "still capable of knowing what he wanted to do".

"I had said to him, 'Do you want to go through with what we're doing?' And he said, 'Sh*t, yeah.'"

Malcolm started getting treatment during his last tour with the band from 2008 to 2010 and during which he had to relearn the very riffs he'd come up with.

It was strange for him, Angus told Rolling Stone, "but he was always a confident guy, and we made it work".

"Renowned for his musical prowess, Malcolm was a songwriter, guitarist, performer, producer and visionary who inspired many," the statement read. "From the outset, he knew what he wanted to achieve and, along with his younger brother, took to the world stage giving their all at every show. Nothing less would do for their fans."

Young founded AC/DC in November 1973 and soon asked Angus to join when they were 20 and 18 years old respectively.

They began national touring in 1974 with singer Dave Evans

Malcolm is survived by his wife O'Linda and two children.

His death comes just weeks after his brother George Young, guitarist for the Easybeats and AC/DC producer, died at age 70.

Tributes started pouring in from around the world, both from the music industry and elsewhere.