Two people remain in critical condition after an explosion at a building site in central Auckland last week.
Five people were taken to hospital from the building site in Wynyard Quarter on the morning of 26 August.
Firefighters at the scene used hoses to treat patients with burns.
It is not yet confirmed what caused the explosion, but reports suggest an LPG bottle hooked up to a barbecue exploded at the Hawkins Construction site about 6.30am on the day.
It is common for construction workers to use portable gas cookers.
WorkSafe started investigating immediately but said that work could take up to 12 months to complete.
In a statement last week, parent company Downer said it was working with authorities to establish what had happened and its immediate focus was on supporting the injured workers, their whānau, and the team on site.
Council of Trade Unions president Richard Wagstaff last week said he wanted to see a full investigation into the incident.
"It's important there be a full and detailed investigation into how this happened and steps are taken to better protect workers."
Wagstaff said the industry had a terrible record of workers being killed or injured on the job, with 11 construction workers killed and 4800 workers injured just last year.
Fire and Emergency said its own investigation into the incident was also ongoing.
The Wynyard Quarter site is being developed by Precinct Properties and Auckland Council's development arm Eke Panuku, where three new office buildings with ground floor retail are planned.
Construction started this year and is due to be completed in 2025.