A 5-year-old boy was seriously hurt and his sister suffered minor injuries Tuesday morning in Torrance when they were hit by a car while crossing a street on their way to school.

The accident happened just before 9 a.m. as the pair crossed Madison Street at a four-way stop at Newton Street in the Walteria section of the city, said Torrance police Sgt. Bob Watt. A man driving a Chevrolet Sonic ran into the children, Watt said, adding that investigators are still trying to determine the cause of the crash.

“Did he blow the stop sign and hit the children? That’s for the investigators to decide,” Watt said. “If anyone saw what happened, please call detectives.”

The driver, who was reportedly trying to make a left turn onto Newton Street, stopped and has been cooperative with police, Watt said.

The boy, who attends Walteria Elementary School, and his sister, who is in sixth grade at Richardson Middle School, were taken to a nearby hospital. Watt said the boy was being treated for “very serious injuries” to his upper torso. Their names were not disclosed, nor was the identity of the driver.

Streets in all directions were closed near the school until the investigation concluded at about noon.

Torrance Unified School District officials sent a letter to parents of children who attend Walteria Elementary notifying them that counselors are available for students.

“Some of you witnessed a car accident this morning before the start of school,” the letter states. “Witnessing a severe car accident can be distressing for young children. For this reason we have called the district crisis team to be available at our site throughout the day.”

Witnesses are urged to call the Torrance Police Department at 310-328-3456.