Four people were killed when a Dallas cowboy bus collided with a van Sunday on an Arizona highway, officials said.

The bus had no players on board and the staffers in the bus emerged uninjured, Arizona Department of Public Safety spokesman Quentin Mehr reportedly said. The vehicles collided Sunday afternoon on U.S. 93 about 180 miles from Phoenix. The crash led to the shutdown of at least one lane of the highway which is the main route between Las Vegas and Phoenix.

“All on the bus came through OK with some bumps and bruises,” Cowboys spokesman Rich Dalrymple said adding that the bus was carrying the franchise’s staff but did not mention how many were on board.

The bus was on its way to Las Vegas for a Dallas Cowboys fan event scheduled for 6 p.m. EDT. Manager of Vegas’ GameWorks entertainment center Charles Cooper said that around 50 to 75 fans were expected to attend the event, which was subsequently cancelled. Many people were already waiting for the event to begin when the president of a Las Vegas Cowboys fan club conveyed the news of the accident, reports said.

The cause of the collision is still unclear and police have not yet released any information regarding the victims.