Officials are investigating if the driver of a car that allegedly ran a stop sign Saturday and crashed into a SUV -- killing a mother and her four children while the father looked on helplessly -- was on medication at the time.

The driver of the Nissan, identified by the California Highway Patrol as Juana Martinez Bejarano, 41, was taken to a hospital with unspecified injuries after she collided with the Ford Expedition in Riverdale, south of Fresno, while going about 60 mph, authorities said.

The collision, which occured about 7 p.m., sent the SUV into a residential front yard, where it burst into flames. 

The 29-year-old mother, who was not immediately identified, and her four children -- 1- and 3-year-old boys and 6- and 11-year-old girls -- were killed. The father, traveling behind the family in a separate car, suffered burns as he broke out windows of the SUV in an attempt to free his family, authorities said.

It was not immediately clear whether the family died of the impact, or of the flames, although CHP Capt. Dave Paris told ABC30-TV it appeared that the driver "tried to get out, but didn't make it."

There was no evidence that drugs or alcohol played a role in the crash, but investigators are looking at whether Bejarano was on medication at the time of the accident, the Associated Press reported. 

The family was reportedly returning from a family birthday party when they approached the intersection of Excelsior and South Marks avenues. That's when the father told authorities he suddenly saw "this flash and he got into the intersection and the car was already on fire," Paris told the news station. 

Witnesses described how they had to pull the husband away from the burning wreckage as he tried to rescue his family.

"Nobody was moving, nobody was screaming, nobody was crying," Robert Pierce told the Fresno Bee, adding that the car was engulfed in flames up to 15 feet high.

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