Apartment prices in Sydney and Melbourne will fall between 15 to 20 per cent over the next two years, AMP Capital's chief economist Shane Oliver said in his latest property insights to investors on Tuesday.

Dr Oliver told investors apartments were more vulnerable than houses as an investment, because "there was a massive multi-dwelling building boom going on in Brisbane, Sydney, Melbourne and Perth".

"There's a real risk of oversupply. I wouldn't be surprised to see outright price falls in apartments in Sydney, Melbourne, Brisbane and Perth," he said in his note.

AMP chief economist Shane Oliver. Jim Rice

"So people are better off waiting until the dust settles to see if there are any opportunities to buy apartments with a lower price tag."

Dr Oliver told The Australian Financial Review the 15 to 20 per cent forecast will vary from "location to location".