It may take weeks or longer for firefighters to fully extinguish the two most destructive fires that have ravaged parts of the Los Angeles area, fire officials warned.

The sheer sizes of those blazes, the Palisades and Eaton fires, have presented a significant challenge. They have charred almost 40,000 acres combined and are still only partly contained.

Difficult weather conditions have also hindered efforts. David Acuna, a battalion chief with Cal Fire, said the persistence of strong winds, and the fact that fires were burning through homes, which can generate intense heat, made containment impossible when the blazes first ignited.

Crews have been trying to establish a boundary around the fires, using trenches, natural barriers and other methods to prevent further spread. But Capt. Erik Scott, a spokesman for the Los Angeles Fire Department, said, “It’s going to be a slow, arduous process.”

The emergence of smaller fires over the last week has further complicated efforts. Of particular concern was the Auto fire in Ventura County, northwest of Los Angeles, which grew to more than 50 acres before being contained. Officials worried about it breaking free again in windy conditions.

These fires have required an immediate response from both air and ground crews to prevent them from growing, Mr. Acuna said, which diverts resources from the larger blazes.

Stopping the fires’ forward progress is only the first step. Firefighters must also extinguish all remaining flames inside the contained area.

Mr. Scott said this second part of the process would also take time. Among other steps, he said, firefighters need to use hand tools to scrape away brush near the burn perimeter and turn over smoldering piles to ensure nothing is hot enough to reignite.

These timelines are not unusual for large fires. In 2018, the Woolsey fire burned through nearly 100,000 acres in Los Angeles and Ventura counties, destroying over 1,600 structures. The fire ignited in early November and was not contained for two weeks. And it took until early January for the fire to be fully extinguished.

The Santa Ana winds that have repeatedly raised the fire danger over the last week have so far proven lighter than anticipated on Tuesday, but forecasters warn that wind speeds could increase on Wednesday. The region remains critically dry, with little rain expected in the near future. The combination of those elements is threatening to ignite more fires across Southern California, and could further hinder firefighters’ efforts.

Erin McCann contributed reporting.