More than 20 people were killed and at least 100 others injured after a gunman opened fire Sunday night at a country music festival opposite the Mandalay Bay hotel and resort on the Las Vegas Strip, authorities said.

University Medical Center spokeswoman Danita Cohen said the hospital is still evaluating the condition of “many patients” with gunshot wounds in the wake of the shooting, but at least 14 were in critical condition.

Police reported that the suspect, a Las Vegas resident whose name was not immediately released, was dead.

“Right now we believe it’s a solo act, a lone wolf attacker,” Las Vegas Metropolitan Police Sheriff Joe Lombardo said.