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A bus nearly split in half after plowing into a sign pole on a California highway, killing five people aboard and closing the road for hours as authorities investigated the deadly crash.

“This is a catastrophic event. … This is almost like a once-in-a-lifetime occurrence,” California Highway Patrol spokesman Moises Onsurez told CNN affiliate KCRA.

The investigation into what caused the crash, he said, will be “very intricate and long.”

The bus made a “turning movement” before slamming into an exit sign pole near Atwater, California, around 3:30 a.m. Tuesday, Onsurez told CNN. The pole sliced halfway through the bus, he said.

“There were people crying and the bus was split open,” 12-year-old passenger Jennifer Rivera told KCRA. “Some man pulled me up because I was stuck.”

The bus was traveling north from Mexico on the way to Washington state, CNN affiliate KFSN reported.

There were about 30 passengers on board. At least six people were airlifted to hospitals, Onsurez told KCRA, and ambulances transported seven others with injuries.

By Amanda Watts and Catherine E. Shoichet