PALO ALTO -- A family of six, including four daughters, met unspeakable tragedy Friday morning when their SUV collided with a California Highway Patrol cruiser, killing one of the daughters and injuring several others and the officer, authorities said.

A 24-year-old San Bruno woman was killed and her sister was critically injured when their SUV flipped and threw them from the vehicle, said Officer Amelia Jack. The CHP officer, described as new to the force, was not seriously injured. The cruiser, like the SUV, appeared to be wrecked and debris including shopping bags littered the roadway.

The crash between the patrol car and a gold Lexus SUV was reported about 6:50 a.m. Friday in the northbound lanes of Highway 101 approaching the Oregon Expressway and Embarcadero Road offramp, according to the CHP.

The officer had pulled over to help a motorist who was changing a tire on a white pickup truck, said Sgt. Diana McDermott. For a reason under investigation, the SUV crashed into the back of the patrol car, sending the SUV off the roadway where it overturned at least once.

"It's unclear why the (driver) drifted off the roadway," McDermott said.

A father, mother and their four daughters from San Bruno were riding in the SUV. The parents and two daughters who remained inside the vehicle after the crash were wearing seat belts and hospitalized for injuries ranging from minor to major, Jack said. The seatbelt status of the deceased woman

and the other woman who was ejected remains unclear.

The officer, who was inside his car when it was struck, suffered minor injuries.

Multiple lanes and the offramp are expected to be closed until at least 1 p.m. as investigators examine the crash site. McDermott said the lengthy closure is essential because once traffic is allowed back on the road, they have no more chances to revisit the scene as it was.

"What's difficult about a freeway is we have a one-time opportunity to get information and evidence," she said.

Traffic is crawling past the site and is backed up as far as Shoreline Boulevard and is expected to worsen as the morning progresses. Motorists are being advised to seek alternate route such as El Camino Real and Interstate 280.

Check back later for updates to this story.

Contact Robert Salonga at 408-920-5002. Follow him at Twitter.com/robertsalonga.