The growing prevalence of private investors risks destabilising the housing market in the Netherlands’ major cities, the Dutch national bank has warned.

More than a fifth of house sales (21%) went to investment buyers in 2017 in the four largest urban areas, a rise from one in eight the previous year. Elsewhere investors account for 9% of sales.

DNB said the trend was leading to increased demand and driving up prices, notably in Amsterdam, where the average houses costs 35% more expensive than in the pre-crisis peak year of 2008. The capital accounted for more than half the €20 bn spent in real estate transactions in 2017.

‘The role played by investors in the housing market cannot be ignored; they form a large group that increases demand for housing,’ said DNB president Klaas Knot.

He added that the bank was not taking a view on whether private investment was desirable. ‘As long as we have a free housing market the DNB is agnostic,’ he said. ‘But we are concerned about people buying houses that they can’t afford.’

Knot said one solution was to accelerate the construction of new houses to ensure that supply keeps pace with demand, citing a shortfall of ‘several hundred thousand homes’, especially in the mid-price sector.

The assessment was part of the DNB’s overview of financial stability, which was published on Monday. The bank said the main threats came from abroad, such as tensions between the United States and China, trade wars, weak economies in Italy, Greece and Turkey and the potential consequences of Brexit.

DNB also said climate change was a potential risk, both because of the increased likelihood of extreme weather events and as a result of measures introduced by governments to reduce CO2 emissions.