Two people died and eight were injured in a crush after a concert by rapper GloRilla in Rochester, New York.
Police said the crowd began to surge and rush toward the exit, possibly when they thought they heard gunshots.
However, there was "no evidence to support a shooting having occurred", Rochester police lieutenant Nicholas Adams told ABC News.
GloRilla, who had finished performing before the incident, said she was "devastated and heartbroken".
The Memphis musician, whose song F.N.F. (Let's Go) was nominated for best rap performance at last month's Grammy Awards, said she did not hear about the crush until she left the venue.
"My fans mean the world to me," she wrote on social media. "Praying for their families and for a speedy recovery of everyone affected."
Police said the incident began shortly after the concert ended at the Armory venue on Sunday night.
"There are some reports that shots were heard, causing the crowd to panic, but that has not been confirmed," said police chief David M Smith.
The police department added in a statement: "We are hearing many reports of potential causes, including crowd size, shots fired, pepper spray and more.
"Preliminary reports from people at the scene indicate that these injuries were caused from being trampled. We do not have any evidence of gunshots being fired or anyone being shot or stabbed."
Police found three badly injured women inside the auditorium. One, Rhondesia Belton, 33, from nearby Buffalo, died in hospital.
"Her family, friends, and colleagues are devastated and left to mourn this tragic loss," Buffalo Mayor Byron Brown said.
Rochester Police announced the death of a second woman, aged 35, late on Monday. She was named as Brandy Miller by US media outlets.
Another woman remains in critical condition with significant injuries. Seven other people are being treated for injuries that are not life-threatening.
'You got to get up'
On Monday, Rochester news station WHEC-TV interviewed fans as they returned to retrieve personal belongings they had lost in the chaos.
"Me and the girl next to me were climbing on each other trying to get each other up," said Ikea Hayes.
"I was watching the life flash before my eyes and I still didn't know what was going on."
She said she remembered praying and telling herself, "You got to get up. You got to move. If you stay here they're going to keep running you over."
Security guard Anthony Rouse told WHEC-TV he had signed up to work at the concert when he learned his daughter was going.
She was hurt in the rush to the exits and spent part of Monday in hospital, he said. "The whole reason I signed on was to protect her," he said. "And I failed."
Rochester Mayor Malik D Evans said in a news conference that the stampede was a "tragedy of epic proportions".
An investigation has begun into whether the venue's owners had followed the required safety measures.
"When you go to a concert, you do not expect to be trampled," he said. "Your loved ones expect you to be able to come home."
The tragedy comes three months after a deadly crush outside a concert by Afrobeats star Asake at Brixton Academy in London.
Two people died and several more were injured after a large number of people tried to enter the venue.
In November 2021, ten concertgoers were killed after panic broke out at the Astroworld music festival in Houston, Texas.
Last year, 158 people were killed in Seoul, South Korea, at a stampede during Halloween celebrations.