"We're investigating reports of an active shooter near/around Mandalay Bay Casino," police said on Twitter. Several people including a police officer had been shot at a nearby outdoor concert, the Las Vegas Sun newspaper reported.
The Las Vegas hospital was taking in "several" people with gunshot wounds, University Medical Center spokeswoman Danita Cohen told the paper.
Video footage circulating on Twitter purportedly of the Mandalay Bay showed a crowd enjoying a concert before what sounds like volleys of automatic gunfire halt the performance.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)