In a report, The Sacramento Bee said that the victims were found in the county's Berry Creek area.
Addressing a news conference on Thursday night, Sheriff Capt. Derek Bell said: "We're still investigating the circumstances of those (seven) deaths."
The three other fatalities were reported on Wednesday. The identities of the victims have not been released.
According to a latest update from the California Department of Forestry and Fire Protection (Cal Fire) on Thursday night, the North Complex Fire, which is burning across Butte, Yuba and Plumas counties, has grown to 247,358 acres with 23 per cent containment, Xinhua news agency.
The fire has burned more than 2,000 structures, devastating several communities including Berry Creek and Feather Falls, while still threatening others, including Oroville and Paradise.
More than 22,000 structures are still in danger, Cal Fire said.
The massive August Complex Fire raging in the Mendocino National Forest is now the largest blaze in the state's history.
As of Thursday, the fire has burned 471,185 acres, overtaking the 2018 record set by the Mendocino Complex fires, which burned about 459,000 acres.
Overall, the raging wildfires have scorched a record 3.1 million acres of land in the state since August.
The previous record of 1.9 million acres was set in 2018.
Besides California, wildfires are currently raging in nine other western states, including Washington and Oregon.