Amazon's voice assistant Alexa suffered almost an hour-long outage in the US for reasons that remain undisclosed.

Instead of serving up the usual music, news or weather information on request, the voice assistant and smart home gadget appeared stumped for users in several US cities, including New York, Boston and San Francisco on Wednesday, CNET reported.

Throughout the outage period, when users asked Alexa for assistance, it replied: "Sorry. I'm having trouble. Please try in a little while".

The outage was soon resolved but the details about what went wrong remain undisclosed.

"We had an issue that impacted some Alexa customers' ability to interact with the service. The Alexa service is now operating normally," said an Amazon spokesperson.

The users had trouble playing Spotify via Alexa and Google Assistant after an an outage.

"No, it isn't you... It's #Alexa from Amazon. They are experiencing a large outage. No word when she'll be back working," a Twitter user posted.