The van left the roadway Monday on Interstate 15 near Cedar City, Utah, and rolled, ejecting many of the passengers, The Salt Lake City Tribune reported.
Three of the passengers died at the scene, and several others were flown to area hospitals with critical injuries, the newspaper said.
Kristi Christensen, a nurse with Intermountain Medical Center in Murray, Utah, was heading home to Salt Lake City and stopped at the accident immediately after it happened.
"I could tell there were three dead immediately," said Christensen. "I got out and started CPR on one person, but they were gone. I feel awful."
It was not known what caused the van to leave the highway and veer into the median before rolling, authorities said.