Asian investors in Melbourne's central business district have been "stunned" by new rules restricting skyscraper density in the city centre, a planning consultancy that works extensively with overseas firms building apartment towers has warned.

Urbis director Sarah Horsfield said the new rules risked putting "a handbrake on investment".

Ms Horsfield told a Property Council breakfast that the introduction of the one-year interim rules last month had hurt the confidence "of a lot of our Asian investor clients who have been quite frankly stunned that the rules of the game can be so fundamentally changed overnight without any prior warning".

But the government insists that billions of investment dollars are expected to flow into the CBD.