Police Superintendent Tim Anderson said it could take several days to locate all of the bodies, after a mountain of dirt and debris tumbled onto a campsite in Mount Maunganui on Thursday.

Anderson said it was "heartbreaking" that six people remained unaccounted for, including a 15-year-old, after camper vans, caravans and a shower block were buried in a mudslide brought on by heavy rain.

For the past two days, the holiday town in the northern part of the country has staged a series of vigils, holding out hope that the search and rescue personnel would be successful.

Anderson said however it had become apparent there was little chance anyone buried had survived.

"This is heartbreaking news for us and obviously the families involved," he told reporters on Saturday, describing the rescue operation as complex.

"There's still a lot of mud and other aspects, so my primary consideration today is actually the safety of the staff working on it.

"There are really strict parameters around those that are working on site right now."

Prime Minister Christopher Luxon expressed condolences and said the affected families would receive support.

"Police have confirmed fatalities at the campground and the reality that no one would have been able to survive, therefore the rescue operation taking place there is now moving to a recovery," he said in a statement.

"To the families who have lost loved ones - every New Zealander is grieving with you."

New Zealand authorities are facing questions over why people were not evacuated following reports of a landslip at the campsite and neighbouring areas earlier on Thursday.

Two people died in a separate landslide on Thursday in the neighbouring harbourside city of Tauranga.

One of the people killed was a Chinese national, officials said.