Third bus crash in three days injures 20

(CNN) -- At least 20 people were hurt, four of them critically, when a bus crashed Sunday night about 5 miles south of Las Vegas, Nevada, a state trooper said.

Four passengers left the scene with critical injuries after the bus wrecked while traveling north on Interstate 15 about 7 p.m. (10 p.m. ET), said Trooper Kevin Honea of the Nevada Highway Patrol.

Investigators were trying to determine why the bus veered left and hit a guard rail that ripped off its tires and undercarriage. The bus slid into a grassy median, he said.

Estimates of the number of people injured ranged from 20 to 29, he said.

The bus was taking about 30 employees from a resort in Primm, Nevada, back to Las Vegas, Honea said.

Police found tire tread on the roadway and are looking into the possibility that tire failure may have caused the wreck.

"Investigators have a lot of work," Honea said.

The Nevada wreck was the third serious bus wreck in the United States in as many days.

On Sunday morning, four people were killed when a bus carrying more than 40 passengers overturned near Tunica, Mississippi. That bus was carrying passengers to a casino.

Early Friday, a bus crashed in Sherman, Texas, carrying 55 mostly elderly Vietnamese passengers on a church trip. Seventeen people were killed.

CNN's Patty Lane contributed to this report.

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