(ABC News) - Authorities in two California counties are searching for a possible serial shooter responsible for at least 10 drive-by shootings during commuting hours.

The vehicles were struck by gunfire between Nov. 21 and Dec. 17 during the morning and afternoon commuting hours in rural Fresno and Madera counties, said Fresno County Sheriff Margaret Mims in a press conference Thursday morning. Eight of the incidents happened in Fresno County, and two occurred in Madera County.

California authorities are searching for a suspect responsible for at least 10 drive-by shootings in Fresno and Madera counties. (ABC News)

One woman was hurt by shrapnel after her vehicle was shot at while she was sitting inside, Mims said. The victim suffered non-life threatening injuries to her upper torso, Mims said, adding that it could have been much worse.

"If this keeps going, it's going to be a matter of time before we have a murder investigation, and that's what we're trying to avoid," Mims said.

At least 10 cars have been fired upon during a series of drive-by shootings in California's Fresno and Madera Counties, authorities said. (ABC News)

The suspect appears to be shooting at oncoming vehicles driving in the opposite direction, Mims said.

Each of the victims reported hearing "loud bangs" as another vehicle was going past them, often thinking that perhaps another vehicle has "thrown up a rock," Mims said. When they later inspect their vehicles, they find bullet holes in various places.

Authorities are searching for a dark-colored pickup truck with an extended cab or crew, as well as a lifted body and oversize tires, Mims said.

The motive is unknown, and the shots appear to be at random, Mims said, calling the investigation a "top priority." The sheriff asked victims of a drive-by shooting to call 911 as soon as they get to a place of safety, noting that authorities have faced some challenges due to victims waiting too long to report the incident.

"You can imagine with a crime of this nature, with the regularity at which it has been occurring ... we are highly motivated to find out who's doing this," Mims said.

The Madera County Sheriff's Office and the California Highway Patrol are also assisting in the investigation. Crimestoppers has increased a reward for information leading to an arrest to $3,000.

"To the suspect, this is a cowardly act, and we are working very hard to find you," Mims said. "We will hold you responsible."