Patients and staff at Dunedin Hospital, including pregnant women, may have been exposed to asbestos dust.
The Southern district health board revealed last week that asbestos dust particles had been found in ceiling spaces and a basement of three hospital buildings.
Testing has now found the dangerous substance in rooms on four floors of Dunedin hospital's main Clinical Services Building, the health board said.
However, the health board said no asbestos has been found in any air test in the building.
Southern District Health Board chief executive Carole Heatly said swab tests had come back positive for white asbestos dust on four floors of the clinical services building, including radiology and staff changing rooms.
She said a waiting room for ultrasound scans, a corridor and three radiologists' offices had all been closed on the first floor and tests had been done on the other three levels.
"We're awaiting the results of those tests and if any of those tests come back and show a positive result we'll be taking collective and appropriate action, because I say again our first priority is patient, public and staff safety."
Ms Heatly said the risk to patients and staff had been assessed as low or negligible.
All outpatient ultrasound appointments have been cancelled for this week.
The spokesperson for both the Apex Union and the Medical Laboratory Workers' Union, Deborah Powell, told Checkpoint the mortuary, a laboratory, radiologists'offices and a waiting-room have now been cordoned off.
"So those areas have been closed while they are deep cleaned and tested again to make sure they are clear."
Dr Powell said the DHB had been as open as it could.
The Labour party says government delays in replacing the old Dunedin Hospital building were not good enough.
David Clark, Labour's acting health spokesperson and the MP for Dunedin North, said he was particularly worried about staff who have been working in the 50-year-old clinical services building for a long time.
He said he was also worried about delays in the government's plan to replace the building.
"Tony Ryall originally expected a business case before cabinet before the end of this year to replace this building. The current Health Minister said originally there was going to be a business case by the end of next year and now he is saying is that all they would have done by the end of next year is a literature review."
Mr Clark said the people of Dunedin - and others who fly in from across the South Island for specialist appointments - deserved access to quality healthcare.