LOS ANGELES (AFP) - California Governor Arnold Schwarzenegger on Wednesday ordered firefighters to prepare for renewed wildfires ahead of powerful flame-fuelling gusts forecast for next weekend.

Only three of the 23 fires that ravaged California remain active after calm winds and cooler weather allowed firefighters to tame flames which left seven people dead, destroyed 2,000 homes and led to 640,000 evacuations.

But with high temperatures and strong Santa Ana winds forecast for the end of the week, Schwarzenegger has ordered state agencies to pre-emptively deploy staff and equipment to potential high-risk areas.

"It's very important that we remain prepared and alert while there are still fires burning in southern California," Schwarzenegger said.

"This plan helps ensure that resources are strategically placed and standing ready, prepared for whatever the weekend will bring."

Air tankers, tactical aircraft, helicopters and strike firefighting teams fanning out across the state in preparation, a statement said.

Officials meanwhile said Wednesday the deadliest of the California blazes, the 90,440 Harris Fire in southern San Diego County which claimed the lives of five people, was 100 percent contained.

In a separate development, San Diego County officials said all evacuation orders across the district had been lifted.

The causes of the majority of last week's fires are under investigation although it has emerged that an inferno in northern Los Angeles County was started by a young boy playing with a box of matches.

The Buckweed fire which began in the early afternoon of Sunday, October 21, was first blamed on downed power lines, but the investigation later turned into one of suspected arson.

By Monday "detectives identified a male juvenile as the suspect," the Sheriff's Department said in a statement late Tuesday.

"After talking with the suspect, he admitted to playing with matches and accidentally starting the fire. The boy was released to his parents."

The case was presented to the Los Angeles County District Attorney's office "for further action," the statement read.