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THE number of cranes dominating Melbourne's skyline looks set to dwindle as the city's apartment boom fades, figures reveal.

But buyers who owned an apartment over the past 32 years will have seen their investment outperform the stockmarket.

Returns on units and townhouses since 1980 averaged 8.3 per cent a year, compared with 7.3 per cent for the top 200 listed companies, analysis by Oliver Hume Real Estate Group shows.

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''It just shows that the 'set and forget' nature of property can provide excellent returns - but it also highlights the volatile nature of the ASX,'' researcher Andrew Perkins said.

Despite recent concerns that high-rise buildings are dominating the city, the overall number of units being offered to buyers has slumped dramatically. New apartment releases have fallen to only 6900 so far this year to September, well down from last year's peak of 14,400, the figures show.

Oliver Hume predicts a total of only 9000 units will be released this year. Two years ago, 11,200 apartments were on the market.

Not all of those will be built, either, as banks require developers to get at least 70 per cent of a building sold before they release construction funding.

''Things have slowed down without a shadow of doubt in terms of new projects,'' said Robert Papaleo, director of economics firm Charter Keck Cramer.

''After having run so hard for so long, it was going to run out of puff,'' Mr Papaleo said.

A surge in foreign developers and buyers operating in Melbourne had resulted in apartments ''being seen as a global investment opportunity'', he said.

Of the 285 apartment projects under way in Melbourne, about half have begun construction, Oliver Hume's figures show. Several of those are high-profile skyscrapers in the city.

Construction has started on a soaring, 55-level glass tower on the corner of Elizabeth and A'Beckett streets. The architecturally striking, 173-metre-high edifice named MY80 will have a private rooftop nightclub-bar and lounge on the 53rd floor and is being developed by a Malaysian firm, Mammoth Empire Group.

Chinese developer Hengyi Australia has sold more than 70 per cent of a former office at 199 William Street and has started to refurbish the building.

Census data shows multi-unit buildings make up about 26 per cent of Sydney's total housing stock. By contrast, in Melbourne it's only 15 per cent.

''There would seem to be room for further growth in apartments' share in the years ahead,'' Oliver Hume researcher Andrew Perkins said.

Several big projects soon to be finalised will boost the number of apartments available over the next few months, Mr Papaleo said.