Falls in house prices across the country are going to accelerate this year, rating's agency Moody's has forecast, with parts of Sydney and Melbourne likely to face drops of more than 15 per cent over the next 12 months.

Revising downwards its predictions for the nation's property market, the agency on Tuesday said it believed house prices would drop 7.7 per cent through 2019. In January, when it released its first forecasts, it predicted a 3 per cent fall.

Rating's agency Moody's believes house price falls will be larger and more widespread through 2019.

The worsening outlook is largely due to events playing out in the nation's two largest cities.

In January, Moody's forecast Sydney house prices would drop by 3.3 per cent. It now believes the drop will be 9.3 per cent.