GORMAN (CBSLA.com) — A 42-year-old woman and a 6-year-old girl were killed and at least seven other people were seriously injured in a major accident on Interstate 5 early Tuesday morning.

The crash, which happened just after 5 a.m., involved at least six vehicles, including a big rig and a Chevy Tahoe.

The SUV is believed to have rolled over, ejecting the woman and the young girl.

California Highway Patrol officials told KNX 1070 NEWSRADIO it’s not yet known what caused the pileup.

“Looks like these cars were traveling southbound, and for an unknown reason, they collided with each other,” CHP officer Robert Rodriguez said.

Four of those injured — a 65-year-old woman and girls ages 2, 11 and 16 — were air-lifted. Two women and a man were taken to a hospital by ambulance.

“We’re still trying to piece this puzzle together. Everything is being speculated right now. We do know that a vehicle hit a center divide, but we don’t know which vehicle that was. We do know that there were six vehicles total involved, one of them was a big rig. But at this moment, we don’t know if all six vehicles were involved at the same time or if this is in fact two separate crashes,” officer Adriann Garcia told CBS2/KCAL9′s Amy Johnson.

All lanes on the southbound I-5  are now opened after six hours of being closed.