The cause of the outage on New Year's Eve, about an hour long, was not immediately known.
WhatsApp, a popular messaging service owned by Facebook Inc, suffered a global outage for about an hour on Sunday before the problem was fixed.
"WhatsApp users around the world experienced a brief outage today that has now been resolved," a WhatsApp spokeswoman said in an emailed statement.
The cause of the outage, about an hour long, was not immediately known.
In India, its biggest market with about 200 million of its billion-plus users, the app was down just a few minutes past midnight into the new year.
Users in other countries also complained of outages on social media.
WhatsApp is used by more than 1.2 billion people around the world and is a key tool for communications and commerce in many countries. The service was acquired by Facebook in 2014 for $19 billion.