The nature of burns following New Zealand's White Island volcano eruption are so rare they are presenting challenges for expert teams treating the victims, the head of a Sydney burns unit says.

Two more patients wounded in the eruption will be returned home to NSW by Friday evening. Major burns units across NSW and Victoria are already treating 11 other victims.

A survivor of the volcano eruption being removed on a stretcher from an RAAF Hercules at Sydney Airport on Thursday. Credit:AAP

Director of Concord Hospital's burns unit Dr Peter Haertsch said the five patients there had burn injuries which ranged from 7 per cent to 65 per cent of their body.

"The patients were enveloped by a moving cloud of extremely hot gases and also volcanic material such as pumice and dust," Dr Haertsch said.