Online grocer Ocado reported a 30 percent jump in third-quarter sales as it seeks to boost confidence following a turbulent flotation in July.

However, the shares slumped.

Ocado, whose shares are trading 13 percent below an IPO price which had already been cut by almost a quarter from the company's original goal, said it made gross sales of £126.5 million in the 12 weeks to August 8.

Growth was in line with the rate achieved in the first half of its financial year and gross profit margins remained at a similar level to that period, the company said.

Shares in the group, which floated at 180p, fell 6% on disappointment at the figures, falling 9p to 149.75p.

While Britain's store groups are struggling in an uncertain economic recovery, internet retailers are booming as time-pressed shoppers flock to buy goods online.

However Ocado, which sells the products of upmarket grocer Waitrose, has yet to make a pretax profit, and analysts are split whether its model of distributing from a central depot will ever be as cost-effective as filling online orders from local stores, as rival supermarkets do.

The group also faces growing competition, with Waitrose stepping up its own online service and analysts suggesting Morrisons, Britain's No.4 grocer, may unveil a plan to move online in a strategy update on Thursday.

Founded by three former Goldman Sachs bankers in 2000, Ocado raised £200 million from selling new shares in July to fund its expansion. It said on Thursday talks to build a second depot were progressing.

Average orders per week reached 92,834 in the third quarter, up from 70,968 a year ago, while the average order size dipped to £113.59 from £114.73.

At August 8, the group had cash and cash equivalents of £206 million, borrowings of £120 million and undrawn, available loan facilities of £110 million.