"We're about 10-20 per cent overbuilt in some infrastructure assets because of that visitors trade. For example, we have around 20,000 extra sewer [and] water connections."
Mr Rawson said changes in population would be easily accommodated in the city.
He was also expecting a large influx of jobs in the forestry and wood processing sectors in the next 10 years.
Millions of trees currently growing would need to be cut down, Mr Rawson said.
Massey University sociologist Professor Paul Spoonley predicted many of New Zealand's regional areas would struggle in the next 20 years.
"The challenge for regions is how do you keep jobs and how do you keep people?"
According to Statistics NZ, by the time New Zealand's population reaches 5 million in 2026, about 38 per cent of the population (1.9 million) will live in Auckland. He warned that "one industry" towns would face the biggest battle for survival in the next two decades.
Kawerau, which has struggled with high unemployment, job losses and teen suicides, was a prime example, he said.
"When you get job losses and population loss, you lose other services like the local school [and] it becomes a bit of a downward spiral."
Keeping the birth rate high was also important, he said.
One of the biggest challenges facing national population growth was the mass exodus to Australia.
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