Tesco customers have been left unable to shop online as the website and app crashes.
Some would-be shoppers said they were unable to add items to their online shopping baskets.
Others said they could add items - but not remove them.
More customers ran into trouble when trying to book a delivery slot.
Issues began at around 11am today, according to the website DownDetector.
Around 500 shoppers have complained so far.
Around 60% of customers had issues with online shopping, and 23% had issues with the Tesco app.
Tesco shoppers all over the country reported problems, with most of the outages appearing in London.
Customers also took to social media to tell Tesco about the problem.
@Tesco Your website for online orders is broken again. Every time I try to amend an order by adding items, it does it then immediately removes them. Similarly when removing items, they are removed and added back in again. And yes, I have tried logging out and deleting cookies.
— Martok (Andy) (@mart0k)
Tesco has been approached for comment.
On Twitter, Tesco told one customer: "We are experiencing some issues at the moment and are trying to resolve this. Please try again later."
The supermarket added on Twitter: "There's currently an issue with the website that is stopping customers being able to complete basic functions such as booking a slot, checking out an order and amending orders."
Tesco also had a similar problem earlier in August, when customers couldn't add items to their baskets or change orders.
Tesco shoppers started reporting issues with their website at around 5.30pm on August 15 saying it had "crashed".
The issue saw thousands of people unable to shop online or amend their baskets for almost four hours.
Last month Tesco ccustomers were left furious after the supermarket cancelled all home deliveries from 1pm on August 19.
Shoppers calling up Tesco say they got an automatic message that said: "Due to technical issues we’ve had to cancel all orders after 1pm.
"If your order was due after 1pm you have not been charged. We’re unable to reschedule these orders."
Earlier this year Tesco brought in three delivery saver schemes from £2.49 per month.
The lowest-price Anytime Click+Collect option lets shoppers choose when they'd like to collect their shop on orders over £25.
The next monthly tariff is £4.99 for the Off Peak Delivery Plan, this includes a £25 minimum for click-and-collect and a £40 minimum basket price for home delivery.
However, shoppers get the added flexibility of same day slots for click-and-collect and next-day options for home delivery.
And priced at £7.99 a month is the Anytime Delivery Plan. The same minimum spends apply, with same day options for both click-and-collect and home delivery.
