Hundreds of construction workers have returned to the site of the new hospital building in Adelaide this week, despite safety concerns prompting mass walk-offs last week.

It was the last straw for many workers on the new Royal Adelaide Hospital when a crane dropped a load of steel rods on Friday, barely missing workers nearby. 

Reports say it was the sixth incident at the site this year, and unions are worried that severe injuries or death could be just around the corner.

There is a lot of pressure to finish the new hospital as it is one of the largest and most expensive infrastructure projects South Australia has seen, but now runs more than 10 months behind schedule.

The CFMEU (Construction, Forestry, Mining and Energy Union) says rushing will only increase the risk as the tight deadlines already put the safety of 1,200 workers at risk.

Safework SA has launched investigations on six incidents involving cranes at the hospital site, but the union says there have been at least nine “serious” incidents warranting a closer look.

Incidents include collisions of the cranes, falling loads, and a rigger getting his arm caught in a sling and being lifted off the ground.

South Australia’s Industrial Relations Minister, John Rau, has rejected the claims that the tight timeline is to blame for accidents.

The consortium behind the project - Hansen Yuncken and Leighton Contractors - has met with CFMEU officials to work on an agreed for better communication with workers, training, and increasing safe oversight on site.