"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."
