Hotspotting director Terry Ryder said inner Melbourne presented the biggest danger for buyers.
"New supply in Melbourne has gone way over the top but many buyers are unaware of this," he said.
"The danger is that the risks aren't glaringly obvious. In other markets buyers may have a better sense of what they're getting into."
Apartment buyers in inner Brisbane would face a similar problem, with Ryder labelling it the country's second most significant "no-go area".
Sydney's oversupply concerns were more long-term and would be confined to city pockets such as Green Square, the CBD fringe and Parramatta.
"Parramatta, in particular, is a concern," Ryder said.
"There is already a pattern of decline in sales but supply is still increasing. It's a very dangerous combination."
Across capitals, developers' have sought to remedy supply imbalances by targeting foreign buyers, especially from China, in the hope they will absorb excess housing stock.
The strategy wasn't working because Asia-based and local banks were clamping down on foreign lending, Ryder said.
"Someone needs to rent those homes too but vacancies are on the way up in most inner city areas," he said.
BIS Shrapnel analyst Angie Zigomanis agreed foreign buying was decreasing, resulting in softer demand overall.
"Foreign buying was at a peak 18 months ago but it's been in decline since then," Zigomanis said.
Overall, inner city apartment supply was "a cause for concern" across the country but to a different degree in each capital, Zigomanis said.
Inner Sydney would be the only major CBD market where rising supply would not push down prices in the immediate future, he added.