Most of the injuries were fractures, cuts and bruises, Assistant Fire Chief Larry Trujillo said.
The accident occurred at about 10:20 p.m., just after the fireworks ended, Colorado Rockies spokesman Jay Alves said. The display came after the Rockies beat the Arizona Diamondbacks 6-2 before a crowd of 47,032.
"It's like it had no brakes and everybody was just piling up at the end of it. People were just falling on each other," said Cherri Brownfield, who said she was riding down the escalator and was near the bottom when it sped up.
The escalator was carrying fans from the upper level to the street. Alex Frenier, a vendor at Coors Field, said people were screaming and falling down.
"I saw people's heads all hitting each other," he said.
Nick Nossinger was watching the fireworks and saw the accident.
"People were just sliding down like an avalanche," he said.
Paramedics stationed at the stadium began treating the injured and called for help, said Tom Cribley, paramedic supervisor for Denver Health Medical Center. Eight ambulances took patients to four hospitals, he said.
Engineers examined the escalator and found no sign of structural failure, Trujillo said. City building inspectors planned to check for mechanical problems Thursday morning, he said.
Rockies spokesman Jay Alves said Thursday night's game between the Diamondbacks and Rockies will go on as scheduled. He said the stadium's other escalators would be looked over before the game.
Coors Field has six escalators.