An IT glitch on Sainsbury's web site has affected some 10,000 orders since the problem occurred on Tuesday.

The supermarket's web shoppers are greeted with the following message: "We have temporarily frozen our online home delivery website having identified a technical issue and are contacting customers directly whose deliveries have been affected."

The web site is still frozen and the chain could not give a date when the online operations would be back to normal.

In the meantime, rivals Asda and Ocado are announcing plans to fulfil orders from Sainsbury's clients affected by the glitch.

Analysts estimate that the company will lose around £1m worth of sales for every day the web site is unavailable.

Earlier this year, Sainsbury's reported its best online performance ever, with web sales rising by 40 per cent in the last quarter of 2007 and 90,000 orders in the run-up to Christmas up more than 50 per cent on the year before.

And web operations are a key focus area for the chain's multimillion-pound revenue protection programme, which will aim to increase online security and detect fraud before the payment stage.