Scorched trees and burned vehicles and the remains of homes cover the landscape Thursday Sept. 17, 2015, in Anderson Springs, Calif. The Valley fire that sped through Middletown and other parts of rural Lake County, less than 100 miles north of San Francisco, has continued to burn since Saturday despite a massive firefighting effort.

Image Credit: Paul Kitagaki Jr./The Sacramento Bee via AP

MIDDLETOWN, Calif. - The tally of homes destroyed by two massive Northern California wildfires topped 1,000 Saturday after authorities doing damage assessments in the Sierra Nevada foothills counted another 250 houses destroyed by flames that still threaten thousands of more structures.

California Department of Forestry and Fire Protection spokesman Daniel Berlant said the count of 503 homes destroyed by the blaze burning for more than a week in Amador and Calaveras counties comes as firefighters make progress and damage inspection teams have access to affected areas.

Cal Fire had reported 252 homes destroyed as of Friday night by the week-old fire that has charred 110 square miles (285 square kilometres).

"Some of the homes are tucked back in rural areas so it's taken time to reach them," Berlant said.

The fire, which killed at least two people, was 65 per cent contained but still threatening another 6,400 structures.

A separate blaze in Lake County, about 170 miles (274 kilometres) northwest, destroyed at least 585 homes and burned hundreds of other structures. It has killed three people.

Residents of Middletown, the area hardest hit by the massive wildfire in California, were allowed to return home Saturday afternoon. Evacuation orders for other areas in Lake County remained in effect.

The Lake County fire tore through 62 square miles (160 square kilometres) in 12 hours, causing thousands of residents to flee after it ignited a week ago. About 19,000 people were ordered to evacuate. The blaze had charred 116 square miles (300 square kilometres) and was 48 per cent contained Saturday.

Heat was descending again on the two deadly and destructive Northern California wildfires after a few days of fair and favourable conditions, raising fears that major gains could be undone.

"We're looking at predicted weather of 100 degrees (38 degrees Celsius) for the next couple of days, and at least mid-90s (around 35 C) throughout the weekend," Scott Mclean, a battalion chief with the California Department of Forestry and Fire Protection, said Friday.

That makes it essential that the smouldering remains of the two giant blazes be dealt with as quickly and thoroughly as possible, Mclean said.

"You've got some high temps, high winds that could stir up those ash piles and those ember piles," he said. "We have to do that mop-up to be sure this fire goes to bed."

A number of survivors of the Lake County fire said they never got an official evacuation notice when the danger was at its peak a week ago.

Authorities defended their warnings and rescue attempts, saying they did all they could to reach people in the remote area of homes, many prized for their privacy.

"You may get that notice, or you may not, depending on how fast that fire is moving," Cal Fire spokeswoman Lynnette Round said. "If you can see the fire, you need to be going."

— Associated Press Writers Janie Har in Middletown, Andrew Dalton in Los Angeles and Olga R. Rodriguez in San Francisco contributed to this report.

News from © The Associated Press, 2015