Fire crews in Redding for a time abandoned any hope of containing the flames and instead focused on saving lives.
The Sacramento Bee reports that 25-year-old Jade Ball and 19-year-old Jack Fannin, of Redding, were found with what police said was evidence tying them to several burglaries.
The firefighters killed in the blaze included Don Ray Smith, 81, of Pollock Pines, a bulldozer operator who was helping clear vegetation in the path of the wildfire.
Redding fire inspector Jeremy Stoke was killed in the blaze, though no details were offered on what happened to him.
The dead were identified as 70-year-old Melody Bledsoe and her great-grandchildren, 5-year-old James Roberts and 4-year-old Emily Roberts.
"Under these conditions that we are seeing right now, it's not going to take much for the fire to have the extreme spread that we saw a couple of days ago", he said by telephone after visiting the region.
A Go Fund Me effort launched overnight to help Ed Bledsoe had raised nearly half its $30,000 goal by midday on Sunday.
A firefighter died battling that blaze, with seven people also injured.
"Any one of those factors will make containing a fire extremely hard", Bertelli said.
In Canada, Ontario's Ministry of Natural Resources said on Sunday that there were 39 active fires in the north east of the province, 12 of them out of control.
Authorities on Sunday had not reopened neighborhoods in Redding that were devastated by the flames.
The fire broke out on July 23, 2018, which forced tens of thousands of people to flee from their homes.
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As of 6:33 a.m. Friday, the fire has burned 44,450 acres with 3 percent containment, according to Cal Fire officials.
The Philippine Consulate General in San Francisco is also checking the situation of Filipinos in Redding and surrounding areas to determine whether any of them has been affected by the so-called Carr Fire.
The Ferguson Fire in Mariposa County has burned 53,646 acres and is 30% contained. As of Saturday afternoon, those fires had burned almost 100 square miles (260 square kilometers).
As of Saturday night, ground crews backed by a squadron of 17 water-dropping helicopters had managed to carve buffer lines around just 5 percent of the fire's perimeter, leaving the blaze largely unchecked.
Hundreds of miles to the south, the Cranston Fire grew to 7.5 square miles and about 3,000 residents remained under evacuation orders in Idyllwild and several neighboring communities.
The two fires that started Friday destroyed four homes and were threatening more than 4,500 buildings, said Tricia Austin, another Cal Fire spokeswoman. Cal Fire said 5,012 structures are threatened by the fire.
On Saturday, thousands remained under evacuation orders - and 5,000 buildings remained under threat - after officials said the blaze had nearly doubled in size overnight.
"There's not even anything to pick up", he said.
The conditions the firefighters are facing are unprecedented, a mix of "incredibly hot temperatures, steep terrain and heavy wind".
A vehicle problem ignited the fire July 23, but it wasn't until Thursday that the blaze exploded in size and raced into populated areas west of Redding before entering city limits.
An elderly woman and her two great-grandchildren perished in the devastating Northern California wildfire that raged into its fourth day on Sunday. They added the individual had not complied with an evacuation order. "Within 15 minutes, it burned my house down", he recalled. Damante said the "quickness" and "volatility" of the blaze was unlike anything she had ever seen before.