Issues with the Facebook-owned app, which is used by 1 billion people worldwide, included sending and receiving messages and logging in, the Independent reported.
According to monitoring website Down Detector, hundreds of people complained about the outage from Malaysia to Spain, which appeared to have started on late Wednesday evening.
Some users took to Twitter, threatening they would migrate to rival messaging services because of the second outage in as many weeks.
"Around half of complaints (56 per cent) this time around were related to connection issues, while 32 per cent of those who logged problems with the site said they were having trouble receiving messages," Down Detector noted.
The affected users had posted the malfunction cases on social media. Many of them reported later the return to normal service, Xinhua news agency reported.
Other severely affected countries included Belgium, the Netherlands, and Britain.