Winston Peters has vowed to turn Immigration NZ upside down until he gets answers on how New Zealand's population is growing.
Data from the 2018 census shows a net migration figure of 259,000 people over the five-year census period, far higher than the 59,000 from the last seven-year census period.
Peters told The AM Show he's eager for answers from Immigration NZ about how decisions are being made.
"When we try and trawl down an immigration department as to the granular detail upon which you can make decisions, you get some extraordinary results we're trying to fix up as we speak.
"I'll give you one, if I come back from overseas as a New Zealander, been away for 10 years, I'm regarded as an immigrant.
If you start at that most basic, moronic, decision where do you go from there?
"So we are going to find out what's exactly happening with precision and we intend to turn this department upside down until we get those accurate answers."
The Salvation Army is warning housing isn't keeping up with the population boom in wake of the record figures.
"A lot of people we're seeing are still struggling to get the kind of housing they need," the Salvation Army's Lieut-Colonel Ian Hutson told Newshub.
"What we've seen is people going without food, insecure housing, and people having to move around because they can't find the right thing."
Peters said in a post-Cabinet conference on Monday immigration needs to slow and there's needs to be work on the "supply-side" for housing.
He told The AM Show on Tuesday he wants to ensure immigration is at a level that "upskills" businesses and thinks 35,000 a year is a good number, higher than the 10,000 a year New Zealand First suggested at the 2017 election.
"If you're getting to the best people, going to the right jobs and they're regionally based as well, there possibly are somewhat 35,000."