The DHB made the announcement this afternoon, in line with the country's move to Red on the Covid-19 traffic light system.
It said while there was still no confirmed transmission of the Covid variant Omicron in the district, wearing medical masks would ensure a better standard of protection.
“People should also continue to practice physical distancing which means staying at least one meter away from people you don’t know.”
The Southern DHB recognises that not all patients and visitors will have access to medical grade masks.
“Medical masks will be made available for all patients, visitors and staff in both clinical and non-clinical settings,” the DHB's chief operating officer, Hamish Brown, said.
“All patients are required to wear medical masks unless they have a mask exemption or are physically unable to for clinical reasons.
"Visitors are asked to wear a medical mask, scan into all areas they visit in the hospital using the QR codes, practice hand hygiene and stay home if they are sick.”
More information regarding mask usage at DHB facilities can be found on the Southern Health website.