NatWest has apologised to customers after its online banking and mobile app went down during the Black Friday sales.

On what was also payday for some people being the last Friday of the month, customers complained about being unable to access their money.

Some also said that money they had transferred between accounts appeared to have vanished.

NatWest was investigating the root cause of the problems, which were reported from just after 9am on Friday.

It said NatWest cards were not affected and could be used by customers as normal.

A spokeswoman for the bank said: "We are aware that some NatWest customers are still experiencing intermittent issues accessing our mobile and online banking.

"We apologise to customers for the inconvenience and are working hard to fix the problem.

"There is no impact on debit cards, credit cards, ATMs, telephone and branch banking services - customers can continue to use these as normal."

A message posted on Twitter by NatWest on Friday said: "Our online banking, mobile app and bankline are currently facing intermittent problems.

"We're working hard getting them back up and running smoothly for you. We'll post an update when we have more information. And remember to contact us if you need urgent help."

Twitter users vented their frustration at the latest problems - with some saying they were unable to see money in their accounts.

One said: "Shocking online banking down again on a Friday. After 10 years of using you

I'm fed up of this I'm changing banks now."

Another wrote: "Transferred my pay day money over to two different accounts and now I have nothing."

And another said: "I'm getting statements my #natwest transfers have gone in but no actual money on my bank balance."

Another Twitter user said they were actually saving money on Black Friday due to NatWest's services being down, writing: "I'm saving tons of dosh because #natwest is down."

Research from Which? released earlier this week found the banking industry suffers around five IT failures each week typically, shutting millions of customers out of accounts and making payments.

Which? found that over the past year, major UK banks suffered 265 IT shutdowns between them that prevented customers from making payments.

TSB recently apologised to its customers after some account holders were left without their salaries as the bank failed to process overnight payments.

Last year, a major IT meltdown left TSB customers without access to services and dragged on for months.