The South Dunedin Countdown remained closed on Wednesday after pest controllers trapped close to 20 more rats since Friday. New Zealand Food Safety were also investigating Christchurch's Eastgate Countdown after a video showed a mouse scurrying across uncovered salad.
New Zealand Food Safety deputy director-general Vincent Arbuckle told Morning Report there was no evidence or reports to suggest a wider problem.
"But we will be looking at Woolworths general processes around pest management... I would expect that they'll have those processes under significant review."
Arbuckle said the situation in Dunedin had taken longer to contain than was ideal.
But they had done the right thing closing the store on Friday.
"We expect them to remain shut until such time as they can demonstrate that they've got clear air and they're got that problem fully under control."
He said in Christchurch, it appeared proper procedures were not followed immediately after the mouse was spotted.
However, he said an investigation into what went on was in the "early stages".
"People are right to expect good levels of pest management and hygiene in supermarkets."
Woolworths declined an interview on Morning Report.
Its director of stores Jason Stockill earlier said pest control contractors had been onsite at both supermarkets.
Food safety and high standards of cleanliness remained the focus, he said.
Community response needed
Predator Free Wellington project director James Willcocks told Morning Report getting the whole community on board was important for eradicating rats and other vermin.
"Definitely targeting the issue in the supermarket but also acknowledging these have come from somewhere...If they're large numbers, I think one of the supermarkets was 20 rats, they're obviously breeding in very close proximity. So being able to track down where that area is and eliminating it is key."
Willcocks said rats had proven themselves adept at living in urban areas and warming temperatures were making it easier for them.
As well as traps and lethal devises, his organisation uses cameras and a rodent dog to track down particularly wily vermin.
"When you get down to those last individuals you're almost having to cater to individual preferences... does this rat want KFC, does it want McDonald's, does it want pizza?"