The Las Vegas Police Department says the animals were spotted by residents just after 10:15 a.m. Thursday. One caller reported a chimp atop a vehicle, and another caller reported a primate banging on a police car.
Police sent out tweets calling the animal dangerous and urging residents to stay inside their cars or homes.
The agitated animals were stopped by noon. Las Vegas police say they had no choice but to kill one chimpanzee. The other chimp was tranquilized.
It's not yet known where the two chimps came from or how they got loose.
The Associated Press contributed to this report.