A large building site in Canberra's north has been shut down after authorities discovered work had begun without development or building approvals.

Canberra's building regulator issued a stop work notice on TP Dynamics's work site in Bruce, describing the situation as "unusual" and "troubling".

According to Access Canberra, construction had already begun on the multi-unit site.

The breach comes after 17 building sites in Gungahlin were issued stop work notices three months ago because of non-compliance with building standards.

ACT constructions occupations registrar Ben Green said the case was abnormal.

"It is an unusual thing to see, given the people involved are generally well informed about the processes," he said.

Mr Green also said development approvals could be arranged retrospectively.

"But that will be a matter that would need to be investigated by the owners of that particular property," he said.

"At this stage, our focus is on investigating how this occurred and ensuring it is remedied as quickly as possible."

Mr Green said there were no safety concerns at the site and ACT Worksafe had not been asked to investigate.

Union slams 'ludicrous' circumstances

The building regulator has described the case as "troubling". ( ABC News: Alexandra Alvaro )

CFMEU ACT secretary Jason O'Mara said there were "cowboys" in the construction industry, and that he was surprised a project could get so far underway without approval.

"To go out and have tower cranes set up and [be] halfway through a job without having development and building applications in place is ludicrous," he said.

"This shows the disrespect that some of the builders and developers hold for some of the regulatory authorities in Canberra."

Mr O'Mara said workers would be left out of pocket by the sudden decision to close the site.

"They're not going to be able to start here because the developer and the builder haven't done what they should have done," he said.

"It certainly wasn't this builder's first rodeo, they've built a number of projects around Canberra, they certainly know the process."

Michael Hopkins from Master Builders ACT said he was yet to learn why the developer and builder failed to file the relevant paperwork, but that the process for approving construction in the ACT was complex.

"It certainly is unusual that development would start without the necessary approvals because there can be some serious penalties if that's the case," he said.

"The building and development process certainly is complex."

The ACT Legislative Assembly is currently holding an inquiry into building quality in the territory, while last year the Government was criticised for delays in implementing a suite of building industry reforms.

Earlier today the Government pledged $8.9 million for rapid response officers, which it says will allow for up to 1,000 more inspections and site assessments per year.

TP Dynamics have been contacted for comment.