"The recent initial swab testing which has been carried out in these areas has indicated contamination and the further tests are to determine the source and extent of this."
A memo to staff this week obtained by the Otago Daily Times said contractors would be on site doing more tests in a "number of areas" over the next two weeks.
"This testing will not present any risk to hospital staff, patients and visitors," staff were told.
The survey involved the clinical services building, the lecture theatre block and the Fraser Building. All the board's premises would be checked in due course.
Asbestos has previously been identified in health board buildings.
A building report by Beca, released last year under the Official Information Act to Labour's Dunedin North MP Dr David Clark, said numerous areas and building components contained asbestos.
"While we are advised that this is encapsulated, these areas will need careful consideration [in] any refurbishment," the report last year said.