ST HELENA, CALIFORNIA (REUTERS) - Firefighters aided by diminished winds made significant strides on Monday (Oct 5) against flames wreaking havoc in northern California wine country, as a separate blaze - already the largest in state history - grew to over 1 million acres (404,685ha) burned.

In Napa Valley's wine-growing region, calmer winds prevailed late Sunday and early Monday, helping crews gain some ground over the Glass Fire, after an onslaught of heavy gusts and scorching weather kept firefighters on the defensive over the weekend.

"We're cautiously optimistic we're going to get this thing under wraps pretty soon," Cal Fire spokesman Dave Lauchner said.

This wildfire season has shattered records with state officials putting the blame on global warming.

The August Complex fire in the Mendocino National Forest between San Francisco and the Oregon border surpassed 1 million acres, burning more acreage than all California fires from 1932 to 1999.

"If that's not proof-point testament to climate change, I don't know what is," California Governor Gavin Newsom told a Monday news conference.

The 1-million-acre milestone marks California's first"gigafire," a term coined by academics to describe the growing presence and scope of massive wildfires in the US West.

Wildfires across California have burned well over 1.6 million hectares since January, nearly the total land mass of Delaware and Rhode Island combined, and more than twice California's previous record from 2018.

TWO WINERIES LOST

No serious injuries have been reported in the eight-day-old Glass Fire, but nearly 1,500 homes and other structures have been lost in Napa and neighbouring Sonoma County, including at least two wineries.

The fire erupted Sept 27 near the Napa resort town of Calistoga, some 120km north of San Francisco, in the midst of the region's grape harvest, putting some of Napa-Sonoma's 2020 vintage into question.

The bulk of that acreage was incinerated amid an unprecedented outbreak of wildfires across the entire Western United States this summer, stoked by frequent, prolonged bouts of extreme heat, high winds and dry lightning storms.

Scientists have pointed to the region's incendiary weather, along with supercharged fuel beds overgrown with tinder dry grass and scrub, as consequences of climate change.

California wildfires since January have claimed 31 lives and destroyed nearly 8,700 structures.

The August Complex, sparked by lightning on Aug 17 and now 54 per cent contained, has killed one person and burned two times as much landscape as the next largest California wildfire on record - the 186,155ha Mendocino Complex of July 2018.

Five of California's 20 largest wildfires on record have occurred in 2020, according to Cal Fire.