The Ministry of Justice announced a structural assessment of the 110-year-old building found its tower was at risk of collapsing in a significant earthquake.
Areas near the tower, including the main entrance, the High Court, Courtroom 2, the public toilets, security office, public waiting rooms and offices for lawyers and probation were closed immediately and will be out of bounds for up to a year while the strengthening work is done.
Dunedin judges and their support staff whose offices were near the tower will be moved to accommodation in a nearby building.
An option to lease further rooms in that building will also be taken in case the three remaining courtrooms are unable to cope with the workload.
The announcement follows the closure earlier this month of seven other courthouses - including Oamaru and Balclutha - for earthquake-strengthening.
Ministry of Justice acting deputy secretary of courts Robert Pigou said most of the courthouse was safe to occupy and the tower was in "pretty good condition", but the ministry wanted to bring it up to 67% of the new-building standard as recommended in the building code.
While this was happening, some work would be done on other areas of the building, with the total project to cost up to $3 million. However, the work required was a lot less than might have been, considering most of the building was constructed from unreinforced masonry.
"There was a real concern that the whole thing could be at risk."
Mr Pigou said he discussed the closure with court staff and judges yesterday.
He had had an "excellent discussion" with the judges, who told him they were satisfied the workload could be managed with three courtrooms, despite the extra work the courthouse was handling for Christchurch and the Balclutha and Oamaru courts.
Dunedin had been hosting jury trials for Christchurch, but courtrooms in Christchurch were just about ready to start operating again, which would relieve pressure on places like Dunedin and Timaru, he said.
Staff affected by the partial closure would be relocated to other parts of the building, and the provision of alternative waiting rooms and toilet facilities were being worked out. The main entrance to the building would now be the Dunbar St entrance.
"It's going to be a bit stressful for the first couple of days, while we work through these things. There has been an enormous amount of goodwill [from the staff]," Mr Pigou said.
If, after a month, the three courts were not coping with the workload, the ministry would take an option it had on leasing extra space in a nearby building, where the judges were being accommodated.
Asked why the strengthening work was not done during the $11 million refit of the courthouse 10 years ago, Mr Pigou said since the Christchurch earthquakes, the building standards recommended were a lot higher. It had not been considered an issue back then.
