The death of a rigger on a Darling Harbour barge could have been prevented, with union officials denied access to inspect the construction site in late 2016, the Maritime Union of Australia says.

NSW dad Tim Macpherson, 32, died instantly when a heavy metal beam fell on his torso and crushed him while he was working on the barge off Barangaroo on Wednesday afternoon.

“This was a needless thing that absolutely could have been prevented,” MUA Sydney deputy secretary Paul Keating told said on Thursday.

Mr Keating said he and another official tried to inspect the site in November after receiving a tip-off about unsafe work conditions but were turned away, despite having inspection permits.

“We were stopped from speaking to the workers and inspecting the barge, and that raised the red flags for us straight away.”

Construction giant McConnell Dowell contracted the project to Brady Marine and Civil, a company known for “substandard operations”, Mr Keating said.

Brady Marine and Civil declined to comment when contacted.

McConnell Dowell’s Australian managing director Jim Frith said the company’s thoughts were with the man’s family “at this extremely difficult time”.

“We are providing his employer with all the assistance they need to support his family, and all affected staff are being offered support and counselling,” Mr Frith said in a statement.

Mr Macpherson, from Newcastle, had been working on the project for at least six months.

Workers who saw the tragedy unfold were being offered counselling and support, CFMEU state secretary Brian Parker said on Thursday.

“They’re very distraught. These guys work with each other for long hours together each week, and some of them know each other better than they know their own families and friends,” Mr Parker said.

“One of them, who witnessed the whole thing, was particularly upset and spent the whole night speaking to police about the incident.”

The young father’s family visited him at the site in recent weeks, Mr Parker said.

It’s not yet clear how the accident happened but it’s understood Mr Macpherson was helping a crane driver move the two- to four-tonne beam when it swung into another, causing one to fall and topple on him.

The site was closed off on Thursday as NSW Police and SafeWork NSW investigated.

“SafeWork will be issuing notices to stop work at the site and directing the business to review its systems,” a spokesman said.

There have been at least 1500 accidents or injuries at the Barangaroo site in recent years, Mr Parker said, with Wednesday’s incident the first fatality.