The influential planner responsible for the revitalisation of Melbourne's CBD has warned the city will soon be "beyond reasonable repair" if new laws are not urgently introduced to rein in poor skyscraper development.

Professor Rob Adams, a world-renowned urban designer, has told a government panel charged with overseeing the new building rules for CBD designs that, while it was not too late to preserve the quality of Melbourne, change could not be left any longer.

"If we fail to [put in appropriate controls] the quality of the whole city will incrementally decline and we will have squandered the value and amenity that has been built up over the last 180 years," he said.

"Changing the controls now … is exactly the right time to time to do it. Leave it any longer would possibly open up the city to going beyond the point of reasonable repair."