Ocado has apologised to customers after a systems failure forced it to cancel thousands of deliveries.
The UK's largest online grocer said an "operational failure" at a warehouse caused the problem but that the fault had been repaired and the service had "now returned to normal".
It could not say exactly how many customers were affected.
A spokeswoman said all those expecting a delivery had been or would soon be contacted with an explanation for the problem.
Customers will also receive refunds and compensation where appropriate, although the details have not been decided.
A spokeswoman said: "An operational issue at our warehouse has caused us to cancel a number of orders.
"All customers whose order has been cancelled will have, or will soon receive, a phone call from Ocado customer service at which point they will be able to re-schedule their order. Customers affected will be compensated.
"We apologise for any inconvenience this has caused."
The problem affected orders placed yesterday.