Police in Houston, Texas, have opened a criminal investigation into the deaths at the Astroworld festival on Friday.
At least eight people died and scores of people were hurt after a crowd surge on the opening night of the music event in Houston, Texas.
The victims were between the ages of 14 and 27.
Police are also investigating claims a security officer was injected in the neck while trying to restrain a concert-goer.
Panic broke out after the crowd began to press towards the front of the stage during the rapper Travis Scott’s headline set.
As the crush began causing injuries to people, panic grew and the casualties quickly overwhelmed the on-site first aiders, officials said. Some 300 people were treated for injuries such as cuts and bruises.
Houston Police Chief Troy Finner told a news conference that the investigation would involve the homicide and narcotics divisions.
“We do have a report of a security officer, according to the medical staff that was out and treated him last night, that he was reaching over to restrain or grab a citizen and he felt a prick in his neck,” he said.
“When he was examined he went unconscious. They administered Narcan. He was revived and the medical staff did notice a prick that was similar to a prick that you would get if somebody is trying to inject.”
Houston Fire Chief Samuel Peña said the investigation would review video from the scene and explore the causes of the crowd surge and what had prevented people from being able to escape.
In his first statement since the event on Twitter, Travis Scott thanked the police and emergency services and said he was “committed to working together with the Houston community to heal and support the families in need”.
Later he posted a video message on Instagram, in which he encouraged anyone with information about the incident to contact the authorities.
