A firefighter with a baby on the way was killed while working the California wildfires, authorities have confirmed.

Cory Iverson, a 32-year-old engineer with the California engine strike team in San Diego, died fighting the Thomas wildfire in Ventura County. The blaze is the fourth largest in California history, and has so far burned through 379 square miles (982 square kilometers) of the state.

Officials are investigating the circumstances of Mr Iverson’s death, according to Fire Chief Ken Pimlott of the California Department of Forestry and Fire Protection.

"Anne and I are saddened by Engineer Cory Iverson's tragic death," California Governor Jerry Brown said in a statement. "His bravery and years committed service to the people of California will never be forgotten."

Mr Iverson had been with the state since 2009. He left behind his wife, Ashley, and their 2-year-old daughter. Ms Iverson was pregnant with the couple’s second child, expected this spring.

California fires: in pictures Show all 36 1 /36 California fires: in pictures California fires: in pictures A man watches the Thomas Fire in the hills above Carpinteria, California AFP/Getty Images California fires: in pictures Santa Barbara harbor stands as wildfire burns along the coast during the Thomas Fire REUTERS California fires: in pictures Flames from the Thomas Fire burn in the hills of Montecito, California AFP/Getty Images California fires: in pictures Fire personnel drive along West Lilac Road near Bonsall Rex Features California fires: in pictures The Thomas Fire burns on a hillside behind Lake Casitas in Ventura AFP/Getty Images California fires: in pictures Chatsworth firefighters Zach Reynolds, left, and Steven Salazar clear hot spots at a home destroyed by the Skirball Fire on Casiano Road in Bel-Air Rex Features California fires: in pictures A home is consumed by fire Getty Images California fires: in pictures A mountain lion is removed from a truck. Nearly 200 animals were evacuated from the Wildlife Waystation when the Creek fire started. Rex Features California fires: in pictures Firefighters battle the Lilac fire in Bonsall AFP/Getty Images California fires: in pictures Kalorama Apartments that was partially destroyed in the fire Rex Features California fires: in pictures Inmate firefighters fight a fire in an avocado orchard at the Ojai Vista Farm EPA California fires: in pictures Flames consume a structure as the Lilac fire burns in Bonsai, Calif AP California fires: in pictures Inmate firefighters fight a fire in an avocado orchard at the Ojai Vista Farm EPA California fires: in pictures Firefighters monitor a section of the Thomas Fire along the 101 freeway Getty Images California fires: in pictures Firefighters work to extinguish the Thomas Fire as it burns past the 101 Highway towards the Pacific Coast Highway in Ventura AFP/Getty Images California fires: in pictures Firefighter Dan Whelan is silhouetted against the sun as he battles a wildfire burning near Faria State Beach AP California fires: in pictures A firefighter is working on extinguishing the Lilac Fire Reuters California fires: in pictures Firefighters work to extinguish the Thomas Fire as it burns past the 101 Highway AFP/Getty Images California fires: in pictures A wildfire threatens homes as it burns along a hillside in La Conchita, Calif AP California fires: in pictures A car drives past as the Thomas Fire burns a hillside south of Casitas Springs, California AFP/Getty Images California fires: in pictures Firefighters try to extinguish fire at a house in the Bel Air district of Los Angeles Rex Features California fires: in pictures A burnt-out car is seen at the Bel Air district of Los Angeles Rex Features California fires: in pictures A burning house at the Bel Air district of Los Angeles Rex Features California fires: in pictures Firefighters battle to contain flames to a home on fire in the Bel Air neighborhood of Los Angeles Rex Features California fires: in pictures LA city firefighters try to save a winery storage building that is own by billionaire Rupert Murdoch Rex Features California fires: in pictures A firefighter tries to extinguish fire at a house in the Bel Air district of Los Angeles Rex Features California fires: in pictures A burning house at the Bel Air district of Los Angeles Rex Features California fires: in pictures Los Angeles City firefighter Francisco Martinez protects a home as firefighters battle the Skirball Fire in Bel-Air Rex Features California fires: in pictures The Thomas Fire burns behind trails on Old Baldwin Road in Ojai, California AFP/Getty Images California fires: in pictures Members of the Reinhardt family sort through the remains of their family home after the Thomas wildfire swept through Ventura, California AFP/Getty Images California fires: in pictures Heavy smoke covers the seaside enclave of Mondos Beach beside the 101 highway as flames reach the coast during the Thomas wildfire near Ventura, California AFP/Getty Images California fires: in pictures A family wears face masks as they walk through the smoke filled streets after the Thomas wildfire swept through Ventura, California AFP/Getty Images California fires: in pictures Flames from the Thomas fire burn above a truck on Highway 101 north of Ventura AP California fires: in pictures Trees are seen through the haze at the burnt out Vista del Mar Hospital after the Thomas wildfire swept through Ventura, California AFP/Getty Images California fires: in pictures A woman involved in a traffic accident waits to get towed beside a wall of flames on the 101 highway during the Thomas wildfire near Ventura, California AFP/Getty Images California fires: in pictures The Thomas Fire burns along a hillside near Santa Paula, California AFP/Getty Images

Dozens of police and fire vehicles escorted the fallen firefighter's hearse to the county medical examiner’s office on Thursday.

“Corey is just a great young man and he was somebody who just really loved his job,” Chief Tony Mecha of the San Diego County Fire Department told CBS. “What really hit all of us today is that normally this time of year we’re supposed to be slowing down and spending time with our families.”

The California wildfires have also claimed the life of Virginia Pesola, a 70-year-old woman who died in a car crash while evacuating a threatened area. About 100,000 people have been evacuated since the fires erupted on 4 December. Authorities said almost 1,000 structures had been destroyed in the blaze, which is larger than New York City.

California fires: Six major fires continue to ravage southern California

Firefighters tackling the blaze were working 24- to 36-hour shifts, Santa Barbara County fire spokesman Mike Eliason told CNN. More than 8,000 people are working on the fire-fighting effort, pushing through strong winds and low visibility.

The blaze was about 35 per cent contained by Friday, but Mr Eliason said he expects it to continue burning for weeks.

"Our hearts go out to all the folks who have lost homes already,” Mr Eliason said. “Especially this time of year with the holidays coming, you've got to feel for these folks who've lost just everything.”