The Debenhams website has been overwhelmed by shoppers searching for bargains after the department store chain collapsed.
The firm will launch a huge stock clearance sale on Wednesday at 07:00 as non-essential retailers in England reopen after a four-week lockdown.
But many people complained on Tuesday after being placed in virtual queues with thousands of other shoppers.
“We have been seeing unprecedented levels of visits,” a spokesperson said.
In a bid to keep up with the additional demand, the retailer was forced to implement a queuing system for its website, which promised customers: “We will get you onto the site as soon as possible.”
Some social media users reported as many as 900,000 other customers in the queue for the website.
The company had already been running a 14-day “Black Friday” sales event, with discounts of up to 70% expected from Wednesday onwards in-store and online across clothes and homeware.
For other customers, the website crashed completely on Tuesday evening, either before reaching the virtual queue or having reached the checkout stage for their purchases.
One social media user wrote that they had been given only 30 minutes to complete their shopping online.
“Only problem is once you get in there the homepage keeps crashing. No wonder they’ve gone bust,” they wrote.
Twitter user Danielle Harmer said: “Finally get onto the website, start adding to my basket and then an error message pops up saying my queue number has been rejected and I have to join the back of the queue again! Actually livid.”
All of Debenhams’ 124 UK stores are set to close after the failure of last-ditch efforts to rescue the ailing store chain.
It means all 12,000 employees are likely to lose their jobs when the shops cease trading, unless the administrators do a deal for all of parts of the business.
Some social media users expressed sympathies for those staff members now facing uncertainty. Heather Angus wrote: “If you’re planning to go raid Debenhams with the announcement of them selling off stock, please be kind to their staff. This is awful.”
Debenhams had been in administration since April. It is now set to enter liquidation, also known as winding-up, which means it will cease to exist as a company.
The 242-year-old retailer had already trimmed its store portfolio and cut about 6,500 jobs since May as it struggled to stay afloat.
Hopes of a rescue were crushed after the last remaining bidder for the company, JD Sports, withdrew.
There have been suggestions that JD Sports pulled out of bidding for Debenhams because of the collapse of Arcadia, which is the biggest concession operator in Debenhams, accounting for about £75m of sales.
Tough trading during the coronavirus pandemic proved to be the final blow for both Debenhams and Arcadia, which employ more than 25,000 people between them.
Restructuring firm Hilco will start going into Debenhams stores on Wednesday to begin clearing stock.
Shoppers will still be able to buy items in-store and on the Debenhams website, until all of it is sold.
Anyone who has ordered something on the website, including during the Black Friday sales, should receive it. They should also be able to return these items, under the normal rules, within 14 days, if they do not want them.
The business is also accepting payment cards, such as gift cards. If the business is sold, these cards might continue to be valid.
However, if cards are unspent or items not delivered if Debenhams closes entirely, then shoppers may need to contact their bank, via the chargeback scheme, or their credit card provider (if they spent more than £100 on a single order) to get a refund.