More than 50 WellSouth staff took 400 testing kits to the Alliance Lorneville plant as part of the continued voluntary surveillance testing of asymptomatic people in the community.
WellSouth director of nursing Wendy Findlay said testing ran from about noon to 6pm yesterday and by 3pm, 200 tests had been carried out.
"We’re catching people in between shifts and are expecting to use all the tests today.
"We’re not surprised by the numbers [of volunteers]."
Health staff were split into two groups and 24 workers were tested at one time, which took about 10 minutes per person.
Mrs Findlay said Alliance staff had been "very welcoming to health professionals and keen to participate".
"They [Alliance staff] feel its important that we do this work to know whether there are any pockets of the virus in the community and so they feel like they’re helping out."
Ongoing testing would mean health officials would have a better idea of when it was safest to move from Alert Level 3 to Level 2.
Health professionals had come from Queenstown, Wanaka and Dunedin to help Southland staff carry out testing efficiently.
Alliance Group chief executive David Surveyor said the co-operative wanted to "play its part" in the fight against Covid-19.
Tests would be carried out at the Pukeuri plant near Oamaru next week.