Authorities in Oklahoma say two women were killed and another was hurt when a large rock fell off a semi's trailer and crashed through a vehicle's windshield. 

The accident happened Tuesday on Highway 77 near Pauls Valley, which is south of Oklahoma City. The surviving woman told KOCO that she lost her elderly mother and her aunt. 

“A large boulder piece of rock comes out in the back of the semi,” said Trooper Shayne Ballard with the Oklahoma Highway Patrol. “Fairly large rock, like probably somewhere around 40, 50 pounds.”

The patrol says the two women who died were 83 and 89 years old. 

The semi driver never stopped and may have been unaware of what happened. Ballard said they might have identified the semi involved. 

“We are pretty positive that we've located the truck that was driving the same route this (Wednesday) morning," he said. "Going back and forth from a construction site."

Officials are looking at surveillance video to help their investigation.