The two biggest wildfires ravaging the Los Angeles area have killed at least 10 people and burned more than 10,000 homes and other structures, officials said as they urged more people to heed evacuation orders after a new blaze ignited and quickly grew.

The Kenneth Fire started late on Thursday afternoon in the San Fernando Valley just 3.2 kilometres from a school serving as a shelter for evacuees from another fire. It moved into neighbouring Ventura County but a large and aggressive response by firefighters stopped the flames from spreading.

About 400 firefighters remained on scene overnight to guard against the fire flaring up.

Only hours before the Kenneth Fire roared to life officials expressed encouragement after firefighters aided by calmer winds and help from crews from outside the state saw the first signs of successfully beating back the region’s two devastating wildfires.

The Eaton Fire near Pasadena that started on Tuesday night has burned more than 5,000 structures, a term that includes homes, apartment buildings, businesses, outbuildings and vehicles.

Firefighters were able to establish the first bit of containment on Thursday.

To the west in Pacific Palisades, the largest of the fires burning in the LA area has destroyed over 5,300 structures and firefighters had no containment.

All of the major fires that have broken out this week are located in a roughly 40-kilometre band north of downtown Los Angeles, spreading a sense of fear and sadness across the nation’s second-largest city.

No cause has been identified for the largest fires.

The level of devastation is jarring even in a state that has grown used to massive wildfires.

A large portion of scenic Pacific Palisades has been obliterated. Dozens of blocks in the seaside neighbourhood were flattened to smouldering rubble.

In neighbouring Malibu, blackened palm strands were all that was left above debris where ocean-front homes once stood. (AP)