Thousands of weary firefighters, battling a Southern California wildfire that now ranks as the second-largest in the state's known history, got a little help from more favourable weather on Tuesday amid fresh signs of progress against the flames.

As the Thomas fire rages into its third week in the coastal mountains, foothills and canyons of Ventura and Santa Barbara counties northwest of Los Angeles, officials lifted some evacuation orders, sent some visiting firefighters back home and reported improved air quality.

Firefighters have carved containment lines around half of the blaze's perimeter, but it has still spread by several hundred acres a day since the weekend. In total the fire has scorched 272,000 acres (110,070 hectares) - more than one-third the size of the state of Rhode Island - of drought-parched chaparral and brush.

Increasing humidity and diminishing winds have made firefighters' jobs easier since Monday, although the area remains “critically dry,” a coalition of agencies said in a statement.

But the National Weather Service predicted a pick-up in wind speeds late Wednesday and early Thursday, with gusts of 50 miles per hour (80 km per hour) and occasionally higher. The potential for more gusty conditions will continue at least through Friday, it said.

The wildfire, which erupted on Dec 4, has been stoked by hot, dry Santa Ana winds blowing with rare hurricane force from the eastern desert. More than 1,000 homes and other buildings have gone up in flames and some 18,000 other structures are still threatened.

One firefighter died of smoke inhalation and burns last Thursday near the town of Fillmore, in Ventura County. There were signs of progress on Tuesday, with the firefighting force falling to 8,200 from a peak of 8,500 as officials decided to send personnel from surrounding areas back home, and the once smoky air began to clear. “Ventura County is no longer experiencing unhealthy air quality,” the county fire department reported. “We are at moderate and good levels.”

But coastal communities such as Santa Barbara, Montecito and Summerland remained at risk as crews hurried to extend and shore up buffer zones before higher winds return. Full containment is not expected before the second week of January.

The Thomas fire's destruction is nearing that of California's largest wildfire, the 2003 Cedar fire in San Diego County that consumed 273,246 acres (110,600 hectares) and killed 15 people. The Thomas fire has displaced more than 100,000 people, although authorities in Santa Barbara County lifted evacuation orders for some places and more communities were reopened on Tuesday.

The California Department of Forestry and Fire Prevention has estimated the cost of fighting the blaze at nearly $140 million. The cause is under investigation. The Thomas fire erupted two months after a spate of wind-driven blazes in Northern California's wine country destroyed several thousand homes and killed more than 40 people. That ranked as the deadliest rash of wildfires, and one of the most destructive, in state history.

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