Spark customers in central Auckland are complaining of problems making cellphone calls this morning.

The telco had warned of expected issues in the city - including a "possible three-day outage" - due to network maintenance.

Spark did not immediately respond to a request for comment, but an outage message on its website says: "Mobile customers in Auckland Central may experience a loss of Voice, Data & SMS services (between 24th October 2018 at 07:00 and 26th October 2018 at 22:00, Up to 2 days 15 hours) due to Network Maintenance."

This message appears on Spark's website.