British online bank Monzo appears to be down as of Tuesday afternoon, potentially leaving its millions of customers without access to personal and business bank accounts.

The bank's app was displaying an error message saying "We're experiencing issues" from about midday, with more than 2,000 reports of issues sent to the website Down Detector, which tracks tech problems. The site indicates problems started at about 10am UK time.

Monzo has not yet put out a statement to confirm the issues, but on X it has replied to several customers acknowledging the problems.

"We're so sorry about this, we know this is far from ideal," Monzo said to one customer. "Our team are aware of this issue and working super hard to fix it. We really appreciate your patience in the meantime."

The issues were being experienced by both iPhone and Android Monzo customers who access their accounts exclusively via the smartphone app. Monzo has no brick and mortar stores.

"Your app will not be fully functional - thank you for your patience" said a screen within the Monzo app for iPhone, viewed by Express.co.uk:

A status page on Monzo's website told customers they could still make payments using their Monzo cards, but frustrated customers took to social media to voice their annoyance.

"@monzo Come on, this is not good. Can not access any of my accounts. I have never experienced a single problem in all the years I have been with you, but this is a big f*** up," said @MartiBlagi on X.

"@monzo any timescale? I’ve got a rather urgent payment that needs going out asap, and one coming in that I can’t access!" said @chibs9105.

Not all customers were angry at Monzo though, with many pointing out the usual stability of the banking app.

"Just want to say that even tho my @monzo app isn’t working at the moment I can’t even be angry as in 4 and a half years of being with Monzo it’s been faultless! I’m sure you guys will sort it soon!", said X user @DeanChilds12.

Monzo was one of the UK's first so-called 'challenger banks' that uses an online-first model compared to the country's legacy banking institutions. It gained popularity thanks to biral marketing and its coral orange debit cards, but has grown to having more than 9 million customers.

It has been able to offer full current accounts since 2017, and can also issue business and joint accounts. It has paid tiers for different services, but its basic account is free to set up.

Advantages over regular banks are instant transfers between Monzo accounts and an attractive smartphone app that helps people budget and save their money in 'pots'.