A Hawke's Bay winemaker has shared his experiences of the firefighting frontline in Northern California.

A series of deadly wildfires have been raging since Sunday, killing at least 21 people and destroying more than 2000 buildings in the renowned wine-growing region.

Speaking from his home in St Helena, California, former CJ Pask winemaker Bill Nancarrow said the sky was blanketed with smoke, as far as the eye could see.

"The valley is a couple of miles wide and you can't see either side of it. It's really smokey. We're basically surrounded by fires and smoke."

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The father-of-three, whose family had voluntarily left the area, said he was first learned of the fires on Sunday evening when he saw flames encroaching down the valley towards a friend's house and winery.

"I drove down to see if he was awake and aware of what was going on and ended up staying there. Twelve of us turned up and pretty much saved his house and winery."

The group kept hoses on structures to keep them wet and used a bulldozer to dig out fire roads, he said.

"The fires came all the way down [the hill]. We kept them about 20m from the structures. Properties next door just went up in flames. It was pretty crazy."

Nancarrow, who was schooled at Wanganui Collegiate, spoke of the "utter devastation" felt by the community as entire suburbs were wiped out by flames.

"It's heartbreaking because you know that it's somebody's everything. I've got a lot of friends who have lost everything. Particularly from the Sunday night fires because no one was prepared for it and they started up around 10.30pm."

The 45-year-old, who now works for Goosecross winery in Napa Valley, said many people had mere moments to pack before they evacuated.

"If people got out on time they just grabbed what they could and got out. They lost everything. We all got told to pack bags to grab everything and go."

Nancarrow was among those who chose to stay in the smoke-filled region and do what they could to help others.

"There's some pretty tough and resilient people around here and people are banding together and helping each other out. There's a lot of vineyard management companies -they've got some heavy equipment.

"These guys have been helping cut fire roads and doing what they can and there's also people with shovels standing at their friend's houses, putting out spot fires when they flare up."

He said the region was in the middle of grape harvest, a "huge" time of the year for Napa and Sonoma, and people were trying to go about their daily lives the best they could.

"The trash guys came and picked up the trash and the postman has been delivering mail. People are trying to go about things in a normal way but at the same time people are being advised to not go outside too long because the air quality is so bad with the smoke."

Nancarrow said his grapes had not been burned, but there was a real chance the smoke would taint them.

"You can get smoke taint in the grapes, which basically shows itself in the wine. You make a wine that smells like barbecue."