A WORKER has died and another is in a critical condition after a crane dropped more than a tonne of concrete into an occupied pit at a Melbourne work site.

Victoria Police say the crane was transporting a tub of concrete at the corner of Watts Street and Whitehorse Road in Box Hill, east of Melbourne, shortly after 12pm.

Three men were working in the pit at the basement of the residential building site when the chain holding the kibble - a bucket used to transport concrete on a work site - reportedly snapped.

Two of the men became submerged and trapped under the kibble and buried in the wet concrete. One of those men, who has not yet been formally identified, died at the scene.

"He was struck by the object and he was partially submerged in the concrete," senior intensive care paramedic Gary Robertson said.

"It was wet concrete and obviously as you can appreciate there’s a timeline with that as well, because concrete sets.

"This is not something you ever want to see."

Another worker, a 28-year-old man from Caroline Springs, is in a critical condition at the Royal Melbourne Hospital.

A third worker, a 27-year-old man from Southbank, suffered a broken arm. It’s not yet known how long the men were trapped but workers could be seen desperately shovelling wet concrete from the pit.

CFMEU Victorian State Secretary John Setka said the situation was "madness".

"Absolutely tragic scenes on construction site in Box Hill," he wrote on Twitter.

"Our thoughts are with all involved … this is madness."

Mr Setka told 3AW a "mechanical failure" was responsible for the incident and one of the workers was "under the kibble for a while".

"It’s come down, critically injured one worker, broke two arms of another worker," he said.

"It’s massively chaotic. It’s pretty traumatic, understandably. We’ve got counsellors on the way because a lot of the construction workers will need immediate counselling."

Workers on the site — a 12-storey residential building to be completed after 2020 — have been there since last year.

Witnesses said many workers, including the crane operator, had been seen leaving the site in tears.

Workers at buildings nearby also reportedly watched the distressing scene unfold.

Specialist urban search and rescue teams and 40 firefighters have been on the scene using heavy rescue and high angle appliances.

That included winching the man’s body from the pit to retrieve it.

Assistant chief fire officer Brendan Angwin said "it was an extremely challenging incident" being a building site.

"There’s been a lot of work to retrieve these people from the scene," he said.

Mr Setka said the crane company involved in today’s incident, Clark Cranes, was the same company that closed a Richmond street in July when one of its cranes toppled in bad weather.

"Yes, it’s the same company," he said.

Busy Bridge Road was closed for two days to residents after the construction crane threatened to damage nearby homes.

It is understood the CFMEU has ordered all Clark Cranes - about 80 machines -to stop work across the city.

Clark Cranes is a family-owned company which has been operating in Melbourne for more than 30 years. The company’s website declares its "fleet of cranes come in a variety of sizes, styles, and can lift different loads and weights safely".

News.com.au has approached Clark Cranes for comment.

Witness Colin Perry said he heard the noise first and then saw the crane did not look normal.

"It sounded like something crumbled in and then the crane rope was dangling in the air," he told 9 News.

James Steger, who was studying nearby, said there was "such a loud bang".

"It sounded like a house was being demolished," he told The Herald Sun.

Janine Stevens was at home in Court St, just one street over from the site, when she head the incident.

"I heard this incredibly loud bang," she said.

"Because we’ve got building works all around us I thought it was an everyday building noise, or even thunder."

Motorists have been told to avoid the area and traffic has been diverted away from the busy Station Street intersection.

Whitehorse Rd has been partially reopened to outbound traffic but the left lane remains closed outbound.

WorkSafe is on site scaling the crane to determine what went wrong.