The landslide hit Mount Maunganui on the island's east coast at 9.30am on Thursday, bringing soil and rubble down on the busy campsite.
Two people have died, including a Chinese citizen, China's ambassador to New Zealand Wang Xiaolong said on X.
NZ officials have not provided any details on fatalities, although police have said nine people may be missing, including children.
Families enjoying the summer school holiday were among the campers. Recreational vehicles and at least one structure were crushed, images showed.
Prime Minister Christopher Luxon on Friday visited areas hit by recent flooding.
Local Mayor Mahe Drysdale told Radio New Zealand that while search-and-rescue teams had continued at the campground through the night, there had been no progress in finding missing people.
"That's really hard, and we're here with the families and as you can imagine, just that uncertainty of where they are and when we might have a result is pretty hard," he said.
He said the area remained unstable. Emergency Management and Recovery Minister Mark Mitchell told Radio New Zealand it was a challenging and difficult environment.
Police were checking if some campers may have left without informing authorities.
NZ Police Commissioner Richard Chambers told the New Zealand Herald the scale of the disaster and the risks at the site could delay rescue efforts.
"It could be days and we appreciate that everybody is anxious and waiting for their loved ones, and for some answers but we also have to be very careful," he said.
The landslide happened after heavy rains soaked much of the North Island's east coast earlier this week and caused widespread damage.
A landslide in the neighbouring town of Papamoa killed two people on Thursday, and a man was washed away with his vehicle north of Auckland on Wednesday.
Roads remained closed in some of the worst-hit areas, making some North Island towns inaccessible by land. The civil defence organisation in Tairawhiti District said in a social media post that people were walking over landslides to collect water and food from welfare hubs and warned against this due to fears of further landslides.
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