Police are concerned hackers could be behind a scam targeting Christchurch's ethnic community.

A number of Pakistani immigrants have reported to police that they've received phone calls from someone posing as an Immigration officer, who claims there is an issue with the persons residency and they have to pay a large sum of money or risk deportation.

Detective Sergeant Ross Tarawhiti said it's unclear how the scammer knows who to target, or how they found the victims' cell phone numbers.

"That may well have been through an email hacking system, we don't know. That's why we need to try and gauge how big this problem is within those communities.

"Obviously this causes quite a lot of concern within the ethnic community and that's what we're trying to gauge now, whether it's gone across a number of different ethnic groups."

Detective Tarawhiti said police need to hear from anyone else that's been approached by the scammers so they can piece together how widespread the problem is.