It said this was due to “DNS issues” – the same root cause of the huge Amazon Web Services (AWS) outage last week.
Amazon said AWS was operating normally.
Other sites that were impacted in the UK include supermarket Asda, M&S, and mobile phone operator O2 – while in the US, people reported issues accessing the websites of coffee chain Starbucks and retailer Kroger.
Microsoft said business Microsoft 365 customers experienced problems.
Some web pages on Microsoft also directed users to an error notifications that read “Uh oh! Something went wrong with the previous request.”
The tech giant resorted to posting updates to a thread on X, external after some users reported they could not access the service status page.
While NatWest’s website was temporarily impacted, the bank’s mobile banking, web chat, and telephone customer services remained available during the outage.
The UK consumer organisation Which? said businesses had an obligation to ensure customers were kept informed and supported as services were restored, and to compensate consumers impacted.
“Customers should keep evidence of any failed or delayed payments in case they need to make a claim,” advised Which? consumer law expert Lisa Webb.
“Those worried about missing a bill should contact the relevant company to explain the situation and request that any fees be waived,” Ms Webb added.
Meanwhile, business at the Scottish Parliament was suspended because of technical issues with the parliament’s online voting system.
The outage prompted a postponement of debate over land reform legislation that could allow Scotland to intervene in private sales and require large estates to be broken up.
A senior Scottish Parliament source told BBC News they believed the problems were related to the Microsoft outage.
