Whatsapp is adding the ability to record and send voice messages to its smartphone chat software.

The move will help it compete against Facebook Messenger, WeChat, Voxer and BBM which already offer the function.

California-based Whatsapp has said 300 million people now use its app at least once a month.

One analyst said the addition of voice messages should help the firm boost its popularity in parts of the developing world.

"In south-east Asia, for example India and China, and parts of Africa voice messages are popular as an alternative to typing on phones' English-style keyboards," Neha Dharia, an analyst at telecoms consultancy Ovum told the BBC.

"Also in markets where literacy is low ,Whatsapp will do much better with this service."

Whatsapp is adding the new function to its apps for the iPhone, Android, Blackberry, Windows Phone and Nokia S40 platforms.

This is an unusual move as developers tend to prioritise Apple and Google's operating systems ahead of the others.

The firm makes money by charging users an annual 0.99 cent (64p) fee.

Whatsapp is not putting any duration limit on voice messages sent.

It has designed its software so that recordings automatically play through headphones if they are plugged in, or otherwise through the phone's earpiece when the device is placed next to a user's head and through the speakerphone if held away.

Message creators can also see when their recording has been listened to.

The app still lacks the ability to host interactive voice or video conversations, which is possible on Microsoft's Skype and Blackberry's BBM apps. However, Whatsapp works across more platforms.

"This can also be seen as Whatsapp testing the water for Voip [voice over internet protocol] calls at a later stage," added Ms Dharia.

"That is complicated as different countries have different regulations that it would need to follow. So, Whatsapp might decide its strategy based on the places where it can see voice messages prove most popular."