Graph of price to take-home pay is striking
"It is a gigantic bubble, all the more dangerous as it is spread across France," said Pierre Sabatier, from the consultancy PrimeView.
"It reached a paroxysm in the summer of 2011. There is a mix of incredulity and denial as it starts to burst but there can be little doubt that all levers propelling the market are disappearing."
PrimeView said prices across France have jumped 160pc since 1998, though houshold incomes are up just 35pc. Paris has overtaken New York to become the world's third costliest city at €18,000 (£14,600) per square metre.
Standard & Poor's has told investors to brace for a 15pc correction. Credit Agricole says prices may fall 12pc by the end of next year, expecting a "gradual slide" that could last until 2016.
PrimeView thinks it will be much worse. The price-income ratio was stable from the 1960s to the late 1990s, before exploding over the past 12 years as a perfect storm of demographics, state sweetners and cheap credit led to a 12-year blow-off.
There are parallels with Spain and America but Mr Sabatier said the French twist is a replay of the early 1930s when investors fled stocks after 1929 and rotated into "safe" property. Hence the paradox of rising prices during the Depression. The strange boom did not end until premier Pierre Laval cut rent ceilings in 1935, triggering a long slide.
"Laval's policy change was the catalyst. The same could happen now as austerity forces brutal measures," he said. An array of market props are eroding, including tax relief on some mortages and certain capital gains.