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Houston police have walked back from a claim that an Astroworld Festival security guard was pricked in the neck at the event, potentially with drugs.

Police chief Troy Finner said officers had interviewed the guard, who said he was hit in the head, fell unconscious and woke up at a medical tent.

The initial allegation led officials to look into a possible drug-spiking incident at the Travis Scott festival.

Eight people were killed and hundreds others injured after a crowd surge.

Speaking at a news conference, Chief Finner said organisers were told by police to end the event on Friday night when one person in the crowd was being given cardiopulmonary resuscitation.

But he declined to provide an exact timeline of how events unfolded.

Chief Finner estimated the investigation, which is being led by the Houston police department, could take weeks or months to complete, and said he did not believe an independent probe was needed.

There have been concerns about possible conflicts of interest as the police department deployed about 500 officers to the concert, and because of the relationships Scott, who is from Houston, has with local authorities.

Chief Finner dismissed those worries, saying he had only met the singer twice and that there was no "close relationship" between the two.

The crowd surge began when panic broke out as the crowd pressed towards the front of the stage during the rapper's headline set. About 50,000 people were at the festival at the city's NRG Park complex.

As the crush began causing injuries to people, panic grew and the casualties quickly overwhelmed the on-site first aiders, officials said. Two of the injured, including a nine-year-old boy, remain in a critical condition in hospital.

Investigators are reviewing video from the scene to explore the causes of the surge and what had prevented people from being able to escape. They are also working to interview victims and witnesses.

More than 40 lawsuits have already been filed against Scott and festival promoter Live Nation because of deaths and injuries related to the event.