House prices are forecast to continue rising in Australia's two biggest cities this year and next, a trend that Moody's says is raising the level of risk in the major banks' mortgage portfolios.

As banks look to boost lending to property investors, CoreLogic-Moody's Analytics on Thursday forecast 6 per cent growth in national property prices, and 4.1 per cent growth in 2017.

The forecast growth would make the banks more exposed to any downturn in the property market, especially at a time of near record indebtedness.

A separate note by Moody's published late on Wednesday, highlighted a "re-acceleration" that saw May house price growth of 3.1 per cent in Sydney and 1.6 per cent Melbourne.