Priority visa processing will be given to families of those killed or injured in Friday's Christchurch mosque attacks, Immigration New Zealand says.

Acting Head of Immigration Steve McGill said the agency recognised this was "an incredibly difficult time" for those affected, which included people both here in New Zealand and overseas.

Many of the 50 people killed in New Zealand's worst terrorist attack were foreign nationals with families who are here on temporary visas.

"INZ wants to make things as easy as possible for families to come to New Zealand to lay their loved ones to rest or to support their family members who have been injured," McGill said.

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"These are unprecedented circumstances for everyone and INZ is committed to ensuring we do everything we can to support those who have been affected and make the visa application process as smooth as possible."

McGill said the agency was also working through possible options for those affected who are on temporary visas.

Migrants from Malaysia, Bangladesh, Indonesia, Pakistan, Turkey, India, Jordan, Saudi Arabia are believed to be among those who have either been killed, injured or missing.