Spark's VoLTE connection issue causes 20 per cent of calls to fail

Spark customers have had connection frustrations this morning caused by an issue with the VoLTE system. Photo / File

Spark customers were affected by a nationwide system issue this morning that meant 20 per cent of calls were unable to connect.

The system failure was caused by a breakdown in the VoLTE (Voice over LTE) system, but had now been resolved, a Spark spokeswoman said at 5pm.

The issue was nationwide but did not affect specific customers or areas but affected 20 per cent of calls, she said.

Customers using the 3G network were not affected.

"We apologise to any customers who are impacted and our team are working hard to resolve the issue as soon as possible.

"Landlines and calls to 111 emergency services are unaffected."