Kiwis have found themselves on the receiving end of a cluster of spam calls from unknown overseas numbers.

At the weekend, people reported calls, usually from numbers beginning with 0088 or 002, originating in Chad, north-central Africa, Newshub reported.

The calls are believed to be part of a Wangiri scam - a phone fraud named in Japan, meaning "one ring and cut".

A number appears as a missed call, a number appears on a recipient's phone. Users call the number back, believing they have missed a call. The numbers are either premium rate, or contain advertising messages.

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Vodafone said it registered an increase in Wangiri attempts on its network, but assured customers there had been no security breach.

"In this case the fraudsters have compromised the system that manages interconnect charges internationally (interconnect charges occur when different network operators transfer customer calls across their networks)," the company said.

"The best advice we have for customers is to ignore any calls that you wouldn't otherwise be expecting from unfamiliar country codes. Let them go to voicemail. Do not call the number back."