House prices could tumble by a cumulative 30 per cent over this year and next under the most pessimistic scenario unveiled by National Australia Bank, as it braces for higher defaults caused by the coronavirus crisis.

In the bank's half-year results on Monday, the lender published scenarios setting out the potential economic impact of a "V-shaped" recovery and a more gloomy and prolonged "U-shaped" return to growth.

NAB's results included scenario modelling on the potential economic hit from COVID-19.

The bank's "base case", or V-shaped scenario, assumed house prices would fall 10 per cent this year along with a sharp increase in unemployment, before property prices recovered slightly with a 2.6 per cent increase in 2021.

Under a "severe downturn" scenario, the bank assumed house prices would plunge 20.9 per cent this year and a further 11.8 per cent in 2021, before a 2.5 per cent increase in 2022.