St John says those hospitalised have suffered burn and blast injuries to limbs and airways

Central West district operations manager Stuart Cockburn says victims have been choppered for treatment to five hospitals around the country - Middlemore, Auckland, Waikato, Hutt Valley and Christchurch.

He says the scale and type of injuries are something the organisation hasn't dealt with before, labelling it "unprecedented".

It's understood Victim Support workers spent time with first responders last night, traumatised by what they had seen and heard.