WhatsApp handled a record 64 billion messages in 24 hours as the messaging service, which recently agreed to be acquired by Facebook for $19 billion, continues to demonstrate strong growth.

In an official tweet, the company said it saw 20 billion messages sent (inbound) and 44 billion messages received (outbound) during the course of a single day. The difference in number of inbound and outbound messages is due to WhatsApp enabling messages to be sent to multiple users.

In January, WhatsApp co-founder and CEO Jan Koum revealed that the company was processing 54 billion messages per day (18 billion inbound and 36 billion outbound).

WhatsApp is acknowledged as the world’s most popular messaging app with 450 million monthly active users, with rivals such as LINE, WeChat and Viber also showing impressive growth.

The success of these messaging apps is putting pressure on the SMS revenue of operators as consumers increasingly communicate using mobile internet or Wi-Fi connections.

Juniper Research recently forecast that instant messaging apps will account for three-quarters of all mobile messaging traffic in 2018.

The report suggested that the additional functionality provided by IM messaging over SMS — such as the ability to send messages to multiple users, conduct group conversations and send stickers, emoticons and images — will drive traffic volume for messaging apps.

WhatsApp will soon pose another threat to operators after announcing plans to launch a voice service in the second quarter of the year. Mobile operators still generate most of their revenues from providing traditional voice services.

“We think we’ll have the best voice product out there. It’ll use the least amount of bandwidth and we’re going to optimise the hell out of it,” Jan Koum said at Mobile World Congress.

However, Koum indicated a willingness to partner with operators, as he revealed that WhatsApp is planning a tie-up with Germany’s E-Plus and is keen to work with other operators to generate value for consumers.

Facebook plans to allow WhatsApp to operate as a separate part of the business in much the same way as it has done with photo sharing service Instagram.

Koum reaffirmed the commitment of the mobile messaging service to user privacy once the acquisition is complete, while Facebook CEO Mark Zuckerberg suggested that the messaging service will continue to operate without advertising.

Although WhatsApp is clearly on a roll, it was recently forced to downplay reports alleging that messages sent and received on its service can be accessed by malicious individuals.