Sniffer dogs and rescue teams are at the scene as emergency services try to find anyone trapped in the slip at the Beachside Holiday Park.
In a media briefing at 1pm, Police District Commander Superintendent Tim Anderson said he could not give a precise number of those missing, but "what I can say is it is single figures".
He said it was possible they would find people alive.
Emergency Management Minister Mark Mitchell has this afternoon told The New Zealand Herald there are young people among the missing and it was a "heartbreaking" situation.
Speaking at the 1pm briefing Mitchell said they were still in response mode and it was a "rescue operation".
The slip came down around 9.30am, hitting campervans, cars, tents and a toilet and shower block.
Mitchell said Fire and Emergency New Zealand (Fenz) were leading the search, with police and civil defence on the ground to support.
"We are here to make sure everything that can be done is being done," he said.
Mitchell earlier said Fenz personnel were working to dig people out of the slip.
However, Fenz have since said that no signs of life have been heard since this morning.
Bay of Plenty group manager William Pike said members of the public tried to get into the rubble and heard some voices. The first fire crews to arrive also heard them.
Shortly after, Fenz withdrew everyone from the site due to safety concerns.
No signs of life had been heard since.
Tauranga Mayor Mahe Drysdale said it was possible there would be fatalities.
"It's an evolving situation at the moment, we do have several people that are unaccounted for.
"Fenz and Land Search and Rescue are at the site trying to find those people."
They were working through the list of guests for the park, he said.
Drysdale believed there were people in the ablution block, and said fatalities were possible.
"If you look at the scale of things, it's not a good situation."
A witness, Nix Jaques, was about to walk up the mountain when she heard an incredibly loud noise.
"I turned around and I could see the land coming down on to some structures," she said."There were some vehicles that were moved. It came down on an ablutions block - I believe there were some people in the showers - and it shifted a campervan, there was a family with a campervan."
She spoke to a couple missing a child and tried to help in the early stages but said emergency services arrived quite quickly afterwards.
St John declared a major incident and there police, firefighters and ambulance workers at the scene.
Fenz shift manager Paul Radden said 40 firefighters, including urban search and rescue team, were responding.
The slip was in the southeastern corner of the holiday park.
The Mount Maunganui Surf Life Saving Club was being used as a triage centre and evacuation point.
The rest of the campsite has been evacuated.
The Tauranga City Council said they were still gathering information about the slip, "and the situation is evolving".
"What we know is that several people are unaccounted for. Our thoughts are with everyone who has been affected by this event and their loved ones.
"Right now, our priority is supporting our staff on the ground, emergency services and those affected as best we can.
"The incident is currently being responded to by Police, Fire and Emergency New Zealand and St John.
"Road closures will be in place. We are asking everyone to please stay away and avoid the area."
Two others missing
Police say firefighters are having to tread carefully as they try to find two people missing in another landslide in the Tauranga suburb of Welcome Bay.
Emergency services were called to the incident about 4.15am today.
At least one house on Welcome Bay Rd sustained damage in the slip, and several other homes in the area were evacuated as a precaution.
Police told a media conference that two people were able to escape, but two were unaccounted for.
Supt Anderson said staff were ensuring that the scene was safe.
"We can't put our staff in there if the earth's still moving.
"Obviously, we don't want any more risks or casualties, so it's about working closely with fire and working through that today."
Cordons are in place and people are being advised to stay clear of the area.
Supt Anderson said police were working closely with Fenz and hapū and iwi, and the rescue operation was operating simultaneously with the Mount Maunganui one.
He said the scene at Welcome Bay was posing challenges to staff, with instability proving hazardous to rescuers.
Search to resume
Elsewhere, search efforts are set to resume for a man swept away in a vehicle by floodwaters while trying to cross the Mahurangi River at Warkworth, north of Auckland, yesterday
Police said the search would resume to locate the man, a local in his 40s, once water levels had subsided.
An eagle helicopter was also expected to do a flyover of the river this morning.
Police were in contact with the man's family.
"We acknowledge they must be going through a very uncertain and upsetting time while he remains missing," Waitematā North Police Senior Sergeant Carl Fowlie said.
Earlier, on the East Cape, helicopters were deployed to assist people trapped on roofs due to flooding in Te Araroa, police said.
Seven people were rescued and were being evacuated by helicopter for medical assessment.
In Gisborne, south of Te Araroa, Mayor Rehette Stoltz said even though the rain was easing, there were still dangers out there.
"We need everyone to be mindful, especially when they travel."
Stoltz said Gisborne had seen extensive flooding and teams would be assessing infrastructure today.
Conditions ease
Conditions have eased after a day of torrential rain yesterday, but many roads remain closed. Power was out to thousands of people this morning but is gradually being restored, and states of emergency remain in place in several areas.
By 1.45pm on Thursday MetService had lifted all its severe weather advisories for both the North and South Islands.
Roading crews are inspecting networks across the upper North Island. Photo: Tairāwhiti Civil Defence
Waters receding
Thames-Coromandel District mayor Peter Revell told Morning Report floodwaters were receding and roads were opening.
"There are a couple that are still cut off by flooding, but there have been four of five locations where there have been slips that have blocked the road."
He said rapid impact assessment teams were out assessing the area.
Revell said overnight there were a few evacuations due to flooding and slips, but everyone was safe.
"A priority is to get all roads open again so all people right around the district so people have access to services such as hospitals."
