Every urban housing market in New Zealand is regarded as “severely” unaffordable, a major report has found, despite efforts by the government to address skyrocketing property prices.

The Demographia international housing affordability survey studied more than 300 urban housing markets in eight countries and found housing in New Zealand was now more than seven times the median income, making it out of reach for most.

The country’s housing crisis – which has seen the homeless population grow, and the waiting list for a state house reach record highs – has spread to the provinces, the Act party’s leader, David Seymour, said.

“The effect of this is that even well-paid, professional Kiwis are unable to buy homes in the cities where they work,” he said. “This is a serious threat to productivity, the main driver of our living standards.

“It costs too much and takes too long to build a house. New Zealand is one of the least densely populated countries in the world, but government has driven land prices up with the result that housing has become severely unaffordable.”

Seymour said councils around the country needed to urgently free up land to build more houses as the lack of affordable housing is “a serious threat to the middle-class”.

Demographia classed unaffordable housing as anything more than three times the median income.

The prime minister, Jacinda Ardern, was voted into office in 2017 with a vow to “fix” the housing crisis, but the government’s flagship affordable housing scheme, Kiwibuild, drew the ire of voters after it built only 47 homes in six months.

A homeless person sleeps in a doorway in the Auckland CBD. Photograph: Phil Walter/Getty Images

The housing minister who oversaw the Kiwibuild fiasco was sacked and the new minister, Megan Woods, admitted the scheme had been “overly ambitious”. The target of building 100,000 affordable homes in 10 years has been scrapped.

Community housing providers said that although the government was trying hard they were not yet seeing real changes and working Kiwis were increasingly falling into precarious housing or homelessness.

The opposition spokeswoman on housing, Judith Collins, said Labour had over-promised: “[It] talked a big game on housing but has failed to deliver meaningful change.”

The coastal city of Tauranga, which has seen a huge influx of Aucklanders in recent years, has New Zealand’s hottest market, with housing costing 9.3 times the local median wage.

Tauranga was followed by Auckland at 8.6, then Napier-Hastings, Hamilton, Dunedin, Wellington, Palmerston North and Christchurch.

The port city was also the sixth most unaffordable city in the global survey, which looked at urban housing markets in Australia, Canada, Hong Kong, Ireland, Singapore, the United States and the UK.

The affordable housing markets are all located in the US, the survey found, and include Rochester, Oklahoma city, and Cleveland.

The least affordable global housing markets are located in New Zealand, Australia and Hong Kong.

Hong Kong is the least affordable housing market at 20.8, followed by Vancouver, Sydney, Melbourne, Los Angleles, Toronto and Auckland.

A co-author of the study, Hugh Pavletich, said housing unaffordability was no longer a crisis. It was “a disaster”.

“This survey is a huge wake-up call basically for all involved at central and local government,” Pavletich said.

“It’s a massive social problem.”