"We heard two loud bangs. We all ran over to check on the driver. We saw the cab was filling with smoke so we grabbed a shovel to smash the window and dragged him out.
"He was awake when we got there but he was concussed as. As soon as we smashed the window he started responding better."
Band mate Shayne Taylor said the ordeal had been "shocking".
"Everyone's okay, that's the main thing," he said.
Constable Nick Athberley said it was fortunate the van had been empty.
Police will investigate whether a vehicle fault, driver error or medical complication caused the crash.
The owner of the van, who asked only to be named as Ben, said he ran painting and decorating business, Whipp Exteriors, out of the vehicle.
"It's my business, it's my work van. I own it all and now it's all gone."
The metal band had also been counting on the van as a means of getting to their New Plymouth gig this weekend.
"Now we'll have to suss something else to get up there," Douglas said.
Nearby residents reported losing power after the crash.