Pest controllers are reporting an extended, "rat season" following a long dry spell which has led to a population boom.
Dry conditions and a long hot summer provided perfect breeding conditions for the vermin, which began to appear earlier than usual, causing phone lines to run hot.
"It's been really bad. It's quite unusual to get that amount of activity at this time of year. It started about six weeks ago. It doesn't normally start until much later," Ace Eradicators owner Phillip Johnson said. "I have already used up almost all of my bait stations."
Some of the rats he had dealt with this season were also more brazen with their nesting habits, positioning themselves closer to humans than they normally would.
"I was at a conference a couple of weeks ago and I was telling some of the guys a story about a job I did for an 86-year-old lady, who had seen a big rat in her house. What she didn't realise was that it was nesting behind her fridge and when I moved it there were five baby rats.
"Everyone was quite surprised - you usually get them nesting in the ceiling but not the kitchen, there is too much foot traffic. It just goes to show how bad it's been."
Mr Johnson was not alone. Many more local companies confirmed they to had noticed an influx.
"It's out of nowhere. All of a sudden everyone needs your help with rats," Pests Away owner Ross Howel said. "I have seen a lot of droppings and used a lot of bait."
Target Pest NZ, a nationwide pest eradicator, was handling 20 to 30 callouts a week, with workers reporting larger rodents than usual.
At an Auckland factory this week, owner Norman Kerr removed one weighing about 900g - the biggest he had seen and the size of a small kitten.
The average rat weighs 500 to 600g.
"We've caught a few big rats lately and it's all about the available food they're getting to.
"They've been able to access more food outside, but also inside," he said.
A Hawke's Bay Regional Council spokesperson added that while they do no deal specifically with rats they were aware of the issue, following a high number of calls from the public.
"We have had a lot people ringing in about rats this season, but we encourage them to contact DOC or the District Health Board, depending what it is relative to."
- Additional reporting APN