Probe into fatal Perth uni roof collapse

A major investigation is under way into the "catastrophic failure" at a building site at Perth's Curtin University that left an apprentice construction worker dead and two others injured.

Jonnie Hartshorn, 23, died after falling more than 20 metres when a metal structure supporting the glass roof of the building collapsed on Tuesday afternoon.

Another worker also fell 20 metres and underwent life-saving surgery at Royal Perth Hospital.

He is in a critical but stable condition in intensive care.

A third worker inside the building at the university's Bentley campus who fell about 10 metres is in a stable condition.

Both injured men are in their 20s.

West Australian police and emergency crews overnight retrieved Mr Hartshorn's body after using specialised equipment and calling in engineers to declare the building safe to enter.

A WorkSafe investigation is under way, with a team of six investigators attending the site on Tuesday.

WorkSafe WA Commissioner Darren Kavanagh said there had been a "catastrophic failure".

"We will conduct a thorough investigation to identify the cause," he told 6PR radio on Wednesday.

Premier Mark McGowan said the incident was a tragedy.

"All of us are shocked and saddened by the loss of a young life. We are also concerned for the future of those people who have been injured," he told reporters in Geraldton.

He urged MPs to pass his government's industrial manslaughter legislation which would enforce a maximum penalty of 20 years' imprisonment for workplace deaths.

Electrical Trades Union WA organiser Damian Clancey witnessed the collapse, which happened during a lunch break.

He said there could have been many more deaths and injuries had it happened just five minutes earlier.

CFMEU state secretary Mick Buchan said he had been made aware after the incident of issues with "deflection in the structural steel".

"Those issues were addressed by structural engineers ... (but) I understand that there were some concerns," he said.

"It's 2020. These events should not occur in the building and construction industry."

The building will house Curtin's new architecture school.

Construction began in 2019 and was due to be completed next year.

Head contractor Lend Lease was "deeply saddened" by the incident, the company's building chief executive Dale Connor said in a statement.

Mr Hartshorn worked for ABS Facade, a commercial cladding installation and glazing company with offices across the company, according to his Facebook page.

Students at Curtin laid flowers near the site of the accident and flags were lowered to half-mast.

Mr Hartshorn's partner Kylie Galende paid an emotional tribute to her "soulmate".

"No one had ever seen me as happy as when we are together," she wrote on Facebook.

"A beautiful man was taken from everyone today and it shouldn't have happened."