Facebook has introduced personal digital assistant ‘M’ to rival services such as Siri, Google Now and Cortana.

As Facebook does not have its own OS, the new service will work on its messenger app helping users carry out tasks like making purchases, booking appointments, or sending gifts.

Users will have to tap a button appearing at the bottom of the Messenger app for them to send a note to M.

M’s software will decode the language and continue with follow up questions to understand the requirement of the user, sending updates as the task is completed.

In addition to an automated assistant powered by AI, the tool will be supported by a team of M trainers.

Users will not know if they are helped by a human or a computer, with the creators highlighting that M has no gender unlike Siri and Cortana which have a female voice.

Facebook vice-president of messaging products David Marcus said: "This is early in the journey to build M into an at-scale service.

"But it’s an exciting step towards enabling people on Messenger to get things done."

Marcus also anticipates the service to eventually become sophisticated enough to figure things out on its own.