A "major downturn" in the housing market will see many estate agents forced to shut up shop, property website Rightmove has said.

The search engine declined to predict the likely depth and length of the downturn, but expects a further decrease in numbers in 2009 as home transactions continue to fall.

However, Rightmove shrugged off the gloom with a 63 per cent rise in first-half profits to £19.8 million from £12.13 million last year, and said it should meet full year forecasts.

The company said membership levels had grown by 5 per cent to 19,301 and revenue by 49 per cent, despite the reduced numbers of estate agents and the "severe" downturn gripping the UK housing market.

The biggest increase came from new homes developers, up 16 per cent to 4,022, as firms bolstered their online marketing in an attempt to shift properties.

Managing director Ed Williams said it was likely members were cutting back on print advertising in order to survive the property market downturn.

He added: "We are redoubling our efforts to ensure that Rightmove generates the enquiries from prospective home buyers which our customers so desperately need."

This week, the Nationwide building society said house prices fell almost 2 per cent in August to post their biggest annual drop since monthly records began in 1991.

The Royal Institute of Surveyors said in July that home transactions have slumped to the lowest level since records began 30 years ago.

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