WhatsApp has confirmed it is working on a solution to the problem.
The app crashed at about 8am with people across the country reporting it was down. By 9am users across London and the south east said the service had returned - while others across the midlands and up north suggested it was still playing up.
The outage appears to have hit much of Europe and some areas in Malaysia and Indonesia.
Reports of issues with the app have also come in from China, Saudi Arabia, India, the USA and Sri Lanka. Many users in countries outside of the UK were still reporting it down an hour later.
Panicked users immediately began creating memes to poke fun at each other, as they grappled with the fact they were unable to use the app.
Paddy Power even joined in, as they tweeted a video of comedian Larry David fainting with the caption: "WhatsApp is down folks. This is not a drill."
Rebekah Vardy, Jamie Vardy's wife, is one of many who has complained about the lack of service on Twitter.
She posted: "Ffs WhatsApp not this morning."
Luisa Zissman asked her thousands of followers: "Anyone else #whatsapp down? Or just me? RT if your not working too."
She received dozens of comments and hundreds of retweets.
People have reported they cannot delete or edit their profile image or update their information, and in some cases privacy settings cannot be updated.
Some people have suggested the launch of the iPhone X - today - has crashed the messaging service.
Website DownDetector published a map showing more than a thousand WhatsApp users reporting issues with the app.
The problems started at about 8am this morning, with 60 per cent of customers believed to be having trouble connecting.
Whatsappen, an unofficial Twitter account which reports on WhatsApp, tweeted: "It's not known how long the issues will take. WhatsApp is aware and working on it."
WhatApp went down earlier this year in May, going offline for hours, before the problem was fixed.
