"Everything was blanketed in ash," Russell Clark told TVNZ.
Dozens of tourists were on the island at the time. Six have been confirmed dead. Eight others are feared to have died and about 30 have serious burns.
New Zealand's PM Jacinda Ardern praised the crews of four rescue helicopters.
"Those pilots made an incredibly brave decision under extraordinarily dangerous circumstances in an attempt to get people out," she told reporters on Tuesday.
"To those who have lost or are missing family and friends, we share in your unfathomable grief and in your sorrow."
In his interview, Mr Clark said he and his fellow rescuers had found a "devastating scene" when they landed.
"There was a helicopter on the island that had obviously been there at the time and its rotor blades were off it."
At least 47 people from around the world were on the island at the time of the eruption.