Marks & Spencer has admitted that some products are running short in its stores as it continues to deal with the fallout from a massive cyber-attack.

The retailer said there were “pockets of limited availability” in some shops, as nearly two weeks of disruption to its IT systems affects its stores.

The company has taken the decision to “take some of our systems temporarily offline” as part of its “proactive management of the incident”.

It said on Wednesday: “We are working hard to get availability back to normal across the estate.”

On Friday, M&S was forced to stop taking orders on its website – which accounts for about £3.8m in sales a day – after days of disruption in stores caused by a cyber-attack that has been linked to the hacking collective Scattered Spider.

M&S has also had to pause deliveries of some packaged food items to Ocado, the online grocery specialist it co-owns.

The disruption caused by the hack – and uncertainty over when it will end – has wiped more than £600m off the stock market value of M&S in just over a week.

The retail website closure came after several days of problems in stores where contactless payments and the collection of online orders were hit from Monday 21 April. Contactless payments were restarted late on Thursday.

A separate technical problem on the Saturday of the busy Easter weekend affected only contactless payments.

Shoppers are now able to browse online and shop in M&S’s physical stores using cash or cards. However, some difficulties continue in stores, with gift cards not currently being accepted and poor availability of goods in some areas.

M&S did not say which areas of the country or specific products were affected by the shortages.

Returning goods is only possible at tills in clothing and homeware stores or via post. Food stores are not currently able to accept returns.

M&S has told shoppers on social media that orders placed after Wednesday 23 April will be refunded.

Those expecting to pick up online orders in stores this week that had been placed before Wednesday were told to wait for a “ready to collect” notification email before heading to a store.

Security experts have warned shoppers to watch out for scammers capitalising on the high-profile incident.

The IT problems interrupt a period of strong trading for M&S and many other retailers in the UK as the warm weather boosts spending on clothing and food.

On Tuesday, analysts at the market research company Kantar revealed that spending on groceries at M&S rose by 14.4% in the 12 weeks to 20 April – just ahead of the cyber-attack.

The group is expected to report on its annual sales figures on 21 May.