Around 17,500 people last year visited Whakaari/White Island, according to White Island Tours' chairman Paul Quinn.
The business had grown over a number of years "and last year had about 17,500 visitors," he told TVNZ.
"We take our responsibilities very seriously. We take our health and safety responsibilities very seriously and this is a big tragedy for us," Quinn said, announcing plans for a meeting at the wharenui shortly.
White Island Tours was bought by Ngāti Awa Group Holdings in 2017.
Tours were routinely running despite the safety level being assessed as level two, Quinn said this morning.
Asked if he had experienced sudden and unexpected volcanic activity previously, he said: "Actually I have - 1995 with Ruapehu. That was a level two that day and the ski field was open. I was there at the time and it erupted unexpectedly and fortunately, there were no fatalities."
A hui is about to be held with staff and the wider whānau of relatives, Quinn said.
"Our priority is support for the staff and whānau who are unaccounted for."
Quinn also cited two staff members he knew and who were unaccounted for.
"This is a great loss for Ngāti Awa. We need to regroup," he said.
The Whakatāne-headquartered business was reporting heightened levels of volcanic activity yesterday. Its website is now suspended saying "we are currently experiencing an emergency" and referring people to contact the business directly.
But it has been promoting special school holiday rates and said "All I want for Christmas is a voucher to visit Whak-a-a-ri.... and a pod of dolphins (or three)."
The business warned those booking of dangers.
"Volcanic alert level: Whakaari/White Island is currently on alert level 2," it said, indicating "moderate to heightened volcanic unrest, there is the potential for eruption hazards to occur.
The tour business said it operated through the varying alert levels but passengers should be aware that there is always a risk of eruptive activity regardless of the alert level. White Island Tours follows a comprehensive safety plan which determines our activities on the island at various levels.
Tours cost $229/adult and $130/children under 15 up until next March.
That package included the 60- to 80-minute boat trip on a catamaran, one-hour fully-guided walking tour of the inner crater complex, a light packed snack box, safety gear including a gas mask and hard hat, the permit to land on the island and Department of Conservation permit "to spend time with any marine mammals that we encounter", the company said.
Tourists were told of the chance to see dolphins, flying fish, seabirds and seals which it said were commonly sighted.
The business sold gift vouchers was a Qualmark gold endorsed activity, offering early-morning pickups from Rotorua or Tauranga.
The tours could operate 364 days of the year - every day except Christmas Day, the company said. But not in rough weather.
"The tour is very weather dependent and also numbers dependent. We will confirm with you before 8pm the night prior whether the tour is able to operate," it said.
Due to tides, sea conditions and operational requirements, tour departure times varied. Morning tours generally left between 8am and 10am and, where offered, afternoon tours usually depart between 1pm and 2pm.
Tourists were encouraged to wear fully-enclosed shoes with a good grip. That was a compulsory requirement. They were asked to bring a warm waterproof jacket.
The business has issued a statement saying it was "deeply saddened following the significant eruption at Whakaari / White Island this afternoon.
Quinn's written statement on the tour's Facebook page said: "Devastation is an understatement. This is a terrible tragedy and our thoughts and prayers are with everyone who has been impacted."
The business was now assisting Police and Civil Defence with the official emergency response.