Sydney and Melbourne's housing markets are performing more strongly than expected partly because of the large number of migrants flocking to the country's two biggest cities, a senior ANZ Bank executive says.

The banking giant this week put tough new restrictions on lending for apartments in Brisbane and Perth, but excluded the Sydney and Melbourne markets, which have underpinned the housing boom of recent years.

The bank's Australian chief, Fred Ohlsson, pointed to the potential oversupply of units in Brisbane as one reason for the crackdown, which will bar new lending for customers with deposits of less than 20 per cent of the purchase price.

Thousands of new units are also set to come onto the market in Sydney and Melbourne, but Mr Ohlsson said demand had been surprisingly resilient in these cities, thanks in part to high migration.