Prestigious coastal suburbs have plunged from their recent highs, with the cost to buy a typical home in some spots declining by almost 20 per cent.

New data shows that the property downturn has spread to nearly every suburb in the country’s two largest cities, and is threatening to engulf other centres.

Prestigious coastal suburbs have plunged from their recent highs, with the cost to buy a typical home in some spots declining by almost 20 per cent.