Pest controllers caught 13 more rats over the weekend at a South Dunedin supermarket.
Rats have been an ongoing problem for Dunedin South Countdown for the last few months, and four more were trapped last week.
The store was closed over the weekend to allow pest controllers to have full access. That closure was extended by a further 24 hours for monitoring and cleaning.
A supermarket worker, who asked to remain anonymous, said management was too slow to deal with the issue which had been going on for months.
New Zealand Food Safety (NZFS) deputy director-general Vincent Arbuckle said the rats trapped were of different ages and a further four were trapped overnight.
They were speaking with store operator Woolworths about possibly extending the closure.
Woolworths' director of stores Jason Stockill said two pest control contractors had been onsite with additional traps and cameras, and they believed all the routes rats could get into the supermarket had been sealed.
He said the store would stay closed for a further 24 hours to continue monitoring how effective the pest control had been.
Stockill told Checkpoint on Friday the rodents were not nesting in the store, "they've been coming from out to in".
There was also no evidence the rodents were eating food in the store.
The Ministry for Primary Industries had confirmed it was not a food safety issue, he said.
"I would be confident eating something from the deli there because I know it's not a food safety issue."
The supermarket had lost customers since the rats were found, he told Checkpoint.
"This sort of thing isn't good for our reputation or the local community and we're trying to make sure we do the right thing. We will reopen when we are confident we have disrupted the rodent pattern."
NZFS' Vincent Arbuckle said an experienced food compliance officer was onsite to assist.
"Food safety is our top priority, so we will continue to monitor this situation and take further action, if this is needed."