French media reported that a railing may have given way.
Zdar — whose real name was Cerboneschi — was due to play at the Olympia concert hall in Paris today, to coincide with the release of the new Cassius album, Dreems.
Cassius became a staple of the French electronic scene with their first album 1999 released the same year, which mixed hip hop, house and funk.
Zdar worked in the studio with a galaxy of international stars including the Beastie Boys, The Rapture and Franz Ferdinand, and helped mastermind the acclaimed French electro album, Wolfgang Amadeus Phoenix, which won him and the band Phoenix the best album Grammy in 2010.
Franz Ferdinand's Alex Kapranos hailed him as a "great inspiration, both as a producer, but particularly as a good man and friend".
"His taste was impeccable," the singer-songwriter wrote on Twitter. "He had a huge joy for life, generosity and passion. I will miss him terribly."
Electronic music pioneer Jean-Michel Jarre said Zdar "symbolised everything that was best about music today".
"He was a brilliant iconoclast who at the same time was implacably demanding about sound," he told AFP.
'A TRUE ICON'
Scottish electro star Calvin Harris was one of the first to react to Zdar's death, with fans also taking to social media to express their shock.
"Awful news about Phillipe Zdar, what an unbelievably lovely man with an incredible legacy," he wrote on Twitter.
"I was mesmerised by this record (1999) as a 15-year-old." British electro producer Skream said: "Just woke up … and I genuinely can't believe what I'm reading.
"We spoke not even a week ago and everything was as it always was — a genuine, inspirational chat," said the DJ, whose real name is Oliver Jones.
"The world ya lost a true icon, a visionary," he tweeted.
Zdar formed Cassius in 1996 with Hubert Blanc-Francard, although he and the man who is better known to electro fans as Boom Bass had worked with him since the 1980s.
He was also the owner of the powerhouse Paris studio Motorbass, named after the '90s duo he formed with Etienne de Crecy, another star of the influential "French Touch" house movement.
Zdar, who had three children, is not the first French electro star to die in such tragic circumstances.
DJ Mehdi, who was 34 at the time, died in 2011 after a fall at his Paris home.
Zdar began as a sound engineer for artists such as the legendary French singer Serge Gainsbourg and went on to produce and engineer albums for many stars, including Cat Power's Sun, The Rapture's In the Grace of Your Love and recorded Kanye West on the Cassius-inspired song, Why I Love You.
He made four studio albums with Cassius including Au reve in 2002, 15 Again which marked a turn towards rock in 2006 and Ibifornia in 2016, which featured Pharrell, Mike D and Cat Power.
