Online grocer Ocado has seen shares slump after it warned over a hit to sales following a huge fire which swept through its warehouse in Hampshire.

The group’s shares dropped 6% as it said it would see a fall in sales growth until it can shift operations to other warehouses following the fire at its Andover site, which took more than 24 hours to get under control.

Ocado said the hi-tech robotic warehouse in Andover provides around 10% of its current capacity and its shutdown means there will be a “constraint on our ability to meet our growing customer demand”.

It added: “There will be a reduction in sales growth until we can increase capacity elsewhere.”

Around 200 firefighters have been tackling the blaze which broke out at 2.44am on Tuesday morning and spread overnight, causing substantial damage.

Ocado said part of the roof collapsed, but confirmed no members of the Ocado team or the public were injured.

It said the fire, which started in a corner of the ambient grid, caused substantial damage to the majority of the building and its contents.

But the firm stressed it has comprehensive insurance for the property, stock and equipment and for business interruption losses.

“Once we have had time to assess the damage and prepare a plan to return the CFC (customer fulfilment centre) to operation we will update further as appropriate,” Ocado said.

As well as a human presence, the automated warehouse is staffed by robots that can pack 65,000 grocery orders a week.

The Andover plant is one of four automated warehouses built by the group, which have enabled it to win a number of major international deals providing IT solutions to other retailers.

On Tuesday, Ocado reported a 12.3% rise in annual sales to £1.59 billion, but saw pre-tax losses widen to £44.4 million – against an £8.3 million loss the previous year – due to costs of developing its new warehouses and IT systems.