Supermarket websites have been feeling the strain as customers race to book delivery slots after England was plunged into its third national lockdown.
The Sainsbury's app was under such high demand that the retailer had to temporarily limit access, while there were nearly 15,000 people queuing on the Ocado website and others were reporting problems paying on the Tesco app.
Shoppers at some supermarkets saw empty shelves last night and today, although chains insisted they had good availability and regular deliveries to their stores.
It follows chaos before the first lockdown in March when customers started panic buying items such as toilet roll despite supermarkets urging people to be sensible.
Mother-of-three Lucy Margolis tweeted: 'A perfect summary of this evening: Joining the Ocado virtual queue at position number 4,864, waiting half an hour to enter, and then being completely unable remember what I wanted to add to my shop.'
David Ford from Fleet, Hampshire, said: 'Just tried to log onto Ocado to modify my weekly show and the app says I am 3,671 in the queue.'
And Mark Robinson wrote: 'The only thing increasing more exponentially than Covid cases is the queue on the Ocado website this evening.'
Kirill Korolyov tweeted a screenshot of empty Sainsbury's delivery slots up until January 12, saying: 'I have Covid. How am I supposed to eat if there's no grocery delivery for a week, Sainsbury's?'
Janiede Lang posted a screenshot of nine substitute items on her order with Sainsbury's, tweeting: 'Sainsbury's. This is unacceptable, especially in these difficult times. Never had so many subs from other supermarkets.'
And Judith Brammer from Cleethorpes said: 'Totally fed up with the Sainsbury's app. Delivery now arriving without amendments and I'm locked out of my account. Reset password link arrives three hours later and says it's expired. Great.'
Problems were also reported on the Tesco app, with Nicola Barrett saying: 'Tesco. I'm unable to check out my order for tomorrow.. app keeps freezing at the final saving changes... Help!'
It comes as data revealed today that Britons forked out £11.7billion in supermarkets throughout December in what was the sector's busiest month on record.
Ocado issued a series of responses to customers online, telling one shopper: "I'm really sorry to hear you're having trouble finding a slot. Despite increasing our capacity by 40 per cent this year, slots are being snapped up quickly. We are still updating our website on a daily basis to show our availability."