Middlemore Hospital has begun testing new patients for Covid-19.
Mobile testing teams are offering tests to all patients staying there, even asymptomatic ones, and they will do the same for new patients.
The move was sparked by the investigation into unlinked cases in the outbreak - those with no known connection to current clusters - and to check whether the virus is circulating undetected in South Auckland.
The hospital's chief medical officer Pete Watson said it was part of surveillance testing happening in many parts of the city.
"Although if it is an issue for us if we detect a case, we think it is important we detect all the cases, whether they are in the hospital or the community," he said.
"We are really trying to play our part to support the community surveillance for Covid."
There were between 200 and 300 patients in hospital at the moment, with up to 50 a day likely to be swabbed who otherwise would not have been, he said.
Last week, five Covid-19 patients were treated at the hospital with no idea they had the virus until they were tested there.
One was so sick, he was admitted to intensive care the next day.
Another had abdominal pain, one of the less common but well known symptoms of the virus, and spent hours in a ward with other patients before he was tested.
Since then swabbing in the emergency department has increased and abdominal pain was added to the symptoms potential Covid patients are screened for.
The latest testing is for patients staying in all areas of the hospital, such as those who may be in for cancer treatment or surgery.
People at the emergency department will only be screened if they are admitted to hospital or if they fit the criteria for being tested, Watson said.
That was because the swabbing teams were working during the day for the surveillance testing, but the emergency department went 24/7, he said.
Anyone with Covid-19 symptoms or connections would still be tested and screened.
Watson told Morning Report the hospital was admitting from 100 to 200 people a day, and many were already tested under the hospital's screening system.
Up to 50 a day could be offered a routine Covid-19 surveillance test, in the same way as if they were in the community, where people in seven Auckland suburbs in particular were being encouraged get tested even if they have no symptoms.
"We're almost a barometer of whether there are cases circulating the community, because we are detecting them," Watson said
Watson thought it was unlikely anyone would have the virus, with case numbers continuing to fall.
None of the patients or staff who had been in contact with the five cases last week had tested positive.
The hospital was also offering vaccinations to all patients.