Amazon's Alexa and Microsoft's Cortana will start talking to each other in a first of its kind alliance of rival digital assistants, the companies said on Wednesday.

Amazon Echo device users will be able to ask Alexa to bring in Cortana as a “guest” to tend to tasks such as booking meetings or reading work email.

Meanwhile, those with devices powered by Windows 10 software will be able to have Cortana bring in Alexa for tasks such as controlling smart devices in homes or, of course, ordering items from Amazon.

“There are going to be multiple successful intelligent agents, each with access to different sets of data and with different specialized skill areas,” Amazon Founder Jeff Bezos said in a statement announcing the digital assistants were becoming friends.

“Together, their strengths will complement each other and provide customers with a richer and even more helpful experience.”

Alexa has some 20,000 “skills” created by third-party software developers.

Microsoft chief Satya Nadella has prioritised making the company's software and services available from the broad array of devices people use to connect to the internet.

The latest version of Windows operating software was crafted with that vision in mind.

“Ensuring Cortana is available for our customers everywhere and across any device is a key priority for us,” Nadella said.

“Bringing Cortana's knowledge, Office 365 integration, commitments and reminders to Alexa is a great step toward that goal.”

Alexa and Cortana will begin talking to one another later this year, according to the companies.

The alliance comes in the face of competition from Google and Amazon, which have invested heavily in artificial intelligence infused digital assistants to enhance their offerings.

Siri heading home

Apple this year unveiled a “HomePod” speaker as it moved to challenge Amazon Alexa and Google Home as a smart home and music hub.

HomePod, powered by Apple's Siri digital assistant, will be priced at $349 when it begins shipping in December in Australia, Britain and the United States, the tech giant announced at its annual developers conference in June.

“It's so cool, we really believe it is going to take your home music experience to the next level,” Apple chief executive Tim Cook said of the new device.

HomePod will take Amazon Echo and Google Home, which have been building momentum in the market for voice-controlled speakers capable of controlling smart appliances, fetching content from the internet and more.

HomePod is designed to work with the Apple Music subscription service and can produce rich sound while tapping into the artificial intelligence power of Siri.

Apple Vice President Phil Schiller said the Siri team at Apple had tuned the assistant into a “musicologist” that learns the tastes of listeners and gets songs from the internet cloud.

Amazon has dominated the category of connected speakers since 2014, when it introduced its first Echo, which responds to voice commands and allows users to order goods or rides and control-connected appliances.