A South Dunedin supermarket will remain closed a further 24 hours after pest controllers trapped close to 20 more rats since Friday.
It comes as a new video shows a mouse scurrying across uncovered salad at Christchurch's Eastgate Countdown.
New Zealand Food Safety staff have been on the ground at both supermarkets and confirmed it has launched an investigation into the latest furry problem.
Countdown's owner Woolworths has been fighting to remove rats from South Dunedin Countdown since October, and recently had been confident they were on top of the problem.
But last week, four more rats were trapped, prompting the store to close over the weekend.
New Zealand Food Safety deputy director-general Vincent Arbuckle said Woolworths spent the weekend trying to bring the problem under control, with eight pest controllers on the ground.
"We know that they caught over the weekend 13 rats onsite of various ages and overnight a further four were caught. Their actions are hunting down the problem," he said.
The store would remain closed on Tuesday - it did not open on Monday - to check for and trap any rodents that might be stuck in the store.
Arbuckle said there was no evidence the store had been selling contaminated food.
He was comfortable with the efforts being made by Woolworths to exterminate the problem.
"It's just simply not right to have that level of pests evident in the store that's retailing food. So they are of the same mind that they need to get on top of this problem and they are, and until they get it down to zero, that's the point in which, I think they could safely reopen."
Woolworths director of stores Jason Stockill said two pest control contractors had been onsite with additional traps and cameras.
There was no evidence of nesting in the store, and they believed all the ways for rats to get into the supermarket had now been identified and blocked, he said.
"Our store team work hard every day to maintain our high standards for cleanliness and work closely with pest control services to manage rodent populations that can be found in urban areas."
In South Dunedin, customers have mixed ideas on whether they would return to the store, with some saying the company had lost their business for not speaking about this at the start, while others planned to return once the store reopened.