Apple iPhone users are taking to social media to report a service failure through the phone's messaging app, iMessage.
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Some users have also reported issues with HomeKit and FaceTime video call services however voice calls appear to be unaffected.
The issues appear to only affect some iPhone users.
Messages sent through the app on the morning of May 17 are reportedly slow to send or are not going through to recipients.
A number of users reported the error on Down Detector, which tracks real-time outages on apps and websites.
Outage reports began to spike at 7.30am and by 8am Down Detector had registered more than 13,640 users struggling to send messages through the app.
The company's system status monitoring website shows that iMessage and FaceTime have not yet been flagged by Apple as unavailable.
Almost 80 per cent of error reports on Down Detector said users were struggling to send messages while 18 per cent flagged issues with receiving messages.
Only three per cent of users said their messages were taking a long time to send.