Homes have been evacuated due to the “risk of toxic release or large cylinder explosion” at a large fire sweeping through an Ocado warehouse.
A 500m “exclusion zone” has been set up as firefighters continue to tackle the blaze, which broke out on Tuesday morning.
Deputy chief fire officer Andy Bowers said the evacuation of Walworth Industrial Estate in Hampshire was a precaution to “keep the public safe”.
A “major incident” has been declared.
Mr Bowers said: “We have a risk of a toxic release or a large cylinder explosion.
“We are working extremely closely with all of our partners to keep the public safe.”
Some homes 1.6km away from the site will also be evacuated depending on the wind direction, Hampshire Fire and Rescue Service said.
Residents outside the exclusion zone have been told to “stay put and close doors and windows”.
Test Valley Borough Council said residents who needed to be evacuated would “be informed by emergency services visiting your property”.
But the local authority advised people who were able leave their properties without assistance to do so.
Chief fire officer Neil Odin said the initial small fire had taken a “dramatic turn” early on Wednesday morning and firefighters had to be withdrawn.
“This building is not meant for humans to be interacting with the racking and the storage – it has robots moving racking on to loading bays, so for firefighters trying to get in that high and to make an effective fire-fighting strategy, it has been very difficult,” he said.
Four firefighters have been treated for minor smoke inhalation. No Ocado staff were injured in the blaze.
A rest centre has been set up for evacuated residents at Harrow Way Community School in Andover.
About 200 firefighters spent Tuesday night tackling the blaze, after it was declared a “major incident”.
The fire service said the blaze involved automated packaging machinery.
Residents nearby have been urged to keep doors and windows shut.
Ocado shares have dropped 6% and the retailer has warned of a hit to sales.
The online grocer said it expected a fall in sales until it could shift operations to other warehouses.
More than 30,000 orders are processed by robots at the Andover warehouse each week, but Ocado has not given any detail about what the impact will be to customers.
The grocer has other warehouses, including in Hatfield, Hertfordshire, which have been unaffected. The Andover site accounts for 10% of Ocado’s capacity.
Homes have been evacuated due to the “risk of toxic release or large cylinder explosion” at a large fire sweeping through an Ocado warehouse. A 500m “exclusion zone” has been set up as firefighters continue to tackle the blaze, which broke out on Tuesday morning.