Mayors are in a standoff as New Zealand's most densely populated city threatens to spill its girth into neighbouring districts.

And it's not Auckland.

Hamilton is the most constrained city in the land with nearly 1500 people per square kilometre and the metropolis is feeling the effects of its small land mass.

TOM LEE/STUFF Hamilton Mayor Andrew King says the city is constrained by its boundaries and needs more land.

"Undesirable outcomes" are becoming more frequent, according to the city's Mayor Andrew King.

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Factories and houses are being squeezed into areas that are not suitable and potential employers are staying away because there is no space for large, linear factories.

"We do need to do something," King said.

His solution, as part of a 100-year planning drive, is to spill Hamilton's grow across the borders but he faces stiff resistance.

"[Waipā] are not subdividing or doing anything on our boundary or anything near our boundary that would make it hard for us when we do take it over in the future," King said. "To the north of Hamilton, that's not the case."

Waikato District Council is developing at Hamilton's boundary and it's causing concern.

"In the future, there is no question these areas are going to have to come into Hamilton and when they do come in, we want the planning to have been done in a reasonable way."

Hamilton is NZ's fourth largest city by population, the third smallest territorial authority by area and has the highest population density.

By 2043, its projected population will be more than 244,000 - up from the current population of 168,000

"We've got about 1500 people per square kilometre in Hamilton. There is no other city than Hamilton that has a population base of more than 1000 per square kilometre."

According to the Massey University Healthspace website, Hamilton has a population density of 1436 per square kilometre in an area of 110 square kilometres.

Tauranga has 891 people per square kilometre on 135 square kilometres of land and Wellington has 658 per square kilometre on 290 square kilometres.

Auckland is much roomier with 223 per square kilometre on 4938 square kilometres of land while Christchurch's population density is 241 per square kilometre on 1415 square kilometres.

"In places like Christchurch, you can get in your car and drive for 30 minutes in any direction and your are still inside Christchurch. We're very constrained," King said.

But Waikato Mayor Allan Sanson said a strategic agreement between his council and the city sets out a co-ordinated approach to development.

"Hamilton is barely 100 years old. How the hell can you plan for 100 years? Come on. Get real," Sanson said.

"As long as we do that in a proper fashion, if in the future - and I'm talking decades out - it does come into the city, it will be no different to large parts of Hamilton so once again, I don't know what he's talking about."

Waipā Mayor Jim Mylchreest said without good evidence, the expansion of Hamilton boundaries will be resisted.

"Waipā has always managed the boundary between the city and our own urban areas from early development so there is always a greenfield proposition for the city to expand," Mylchreest said.

"The region needs a good vibrant city and when it's justified, then we would support it but just to take a whole lot of rural land into the city before it is needed would not be in the best interest of either the region or the nation."

Local Government Minister Nanaia Mahuta said the region's growth challenges have been discussed.

"I would encourage a local conversation amongst council leaders and then with the public before any decision is made," Mahuta said.

Application for boundary adjustments must be made to the Local Government Commission.

Population Density 2013-2017

Auckland: 223.5

Hamilton: 1436.3

Wellington: 658.3

Tauranga: 891.7

Christchurch: 241.0

Dunedin: 36.7

Source: Healthspace.ac.nz