House sellers' asking prices plunged by more than £8,000 month on month on average in December, according to a property website.
The 2.6% monthly fall in the price of homes coming on to the market was the biggest recorded in five years, Rightmove said.
Across England and Wales, the average asking price in December was £302,865 - a fall of £8,178 compared with November.
It marked the biggest monthly percentage fall since a 3.1% dip in December 2012.
Rightmove said the dip is "symptomatic of the more challenging market some sellers find themselves in".
In London, asking prices have fallen by 3.7% - or more than £23,000 in cash terms month on month.
In November, the average asking price in London was £628,219 and in December it was £605,203.
The biggest monthly drop in percentage terms was in Wales, where asking prices fell by 5.2% to reach £173,342 on average.
The North East of England was the only region to buck the downward month-on-month trend, with asking prices there up by 1.3% monthly to reach £146,090 on average.
Over the past year, asking prices have increased by 1.2% across England and Wales - and Rightmove predicts that across 2018 asking prices will see an increase of around 1%.
This would be the lowest annual increase since a 0.8% rise recorded in 2011.
Miles Shipside, director of Rightmove, said that every year since 2011 has seen a rise in the price of property coming to market.
He said: "2018 will continue the 2017 trend by being a real mixed bag of different price pressures both up and down, but the net result is that we forecast another year of a slowing in the pace of price rises.
"The peak in the cycle of rising prices was 2015's annual jump of 7.4%. The following year saw price growth more than halve to 3.4%, while 2017 is finishing up at 1.2%."
He said stretched buyer affordability and tighter lending criteria are holding back upward house price pressure.
Rightmove also quoted the views of estate agents.
Mark Manning, director of Manning Stainton in Leeds, Harrogate, Wetherby and Wakefield, said: "Demand across the lower and middle markets remains healthy but there is a little price resistance starting to be felt in various pockets of the region."
Nick Leeming, chairman at Jackson-Stops, said: "Our branches in the West Country foresee an increase in average prices in the middle market, meaning homes valued at £500,000 to £1 million, with some predicting 4% growth next year.
"The Cotswolds will continue to attract families, with those previously based close to the capital increasingly happy to commute further several days a week and work from home in order to achieve their desired lifestyle."