Families 'screamed and cried' in panic when seating collapsed at a circus at Winter Funland.
Some people said they were trapped when around 20 chairs fell 'like dominoes' at the big top at EventCity.
Bosses said three people are understood to have been hurt.
Stephen Shone was sat with his wife and children - aged four and 15 - when chairs fell beneath them.
"There was a bang and the floor just went from beneath us," he said.
"It was terrifying. The floor went from beneath our feet. I remember trapping my arm, but I managed to get it back out.
"I feel like I’ve been hit by a wagon. We’ve all got pains in our backs and legs.
"I was driving home crying, having flashbacks.
"At first we thought it was part of the show, but it wasn’t. We just fell.
"Then there was like a stampede - people climbing over each other trying to get out."
Almost immediately, the lights went off and people tried to navigate their way out of the tent in the dark, witnesses said.
Another woman, who asked not to be named, said she fell to the ground as she was holding her four-year-old granddaughter on her knee.
Her daughter, who was sat next to them, quickly grabbed her granddaughter.
Fellow audience members fell on the woman, aged 44, as the seating behind 'fell like dominoes', she said.
The woman's daughter, who asked not to be named, said: "It happened so quickly. All we heard was a pole crash. The back bit went down first. We were at the front row.
"My little girl was on my mum's knee. My mum fell down. My mum was getting really hurt.
"The stage just went down. Everyone was just falling onto my mum. I was pulling my mum up, and she went down again. I was like 'sh**', panicking.
"My daughter was screaming, she was heartbroken.
'I wish he had not been so trusting': Alex Rodda's mum speaks after death of 'beautiful but naive' son sparks murder investigation
"My mum's leg got stuck. She was trapped for a couple of minutes. The lights went pitch black.
"Everyone was trying to rush out. We got out as quick as we could. (My mum) had to go for first aid.
"She is going to A&E, she has to drive herself. She needs an x-ray. She's just a bit shaken up."
Garry Longthorne, from Bolton, was with his wife, son, daughter-in-law and two grandchildren when he saw the seating collapse.
The 56-year-old said: "There was a massive bang and a crash. We weren't sure what had caused it. We thought the worst. Everything was in pitch black.
"Everyone just had to fend for themselves. We had to use the lights on our phones to navigate our way out."
Police, fire and ambulance crews rushed down to the scene following the incident, which happened at about 6pm.
A spokesman for GMP earlier said they were called to reports of a 'potential seating collapse'.
A spokesman for Winter Funland said a circus performance would go ahead as planned on Sunday, but not in the big top.
Staff will work through the night to set the circus up at a different spot within the venue, he added.
“The health and safety of our customers is a top priority,” the spokesman added.
A full statement read: "There will be a circus performances at tomorrow's sessions (December 15)
"We will be holding these at an alternative venue within the Winter Funland site.
"Today at 6.10pm, during the first circus performance there was a partial collapse of 1 bank of seats, fortunately no one was seriously hurt.
"Three people were assisted by the on-site medical team, with no one requiring hospitalisation.
"An evacuation of the circus area was carried out as per health and safety protocol. The emergency services were called and are working alongside our on-site health and safety officer to commence an investigation."
The Health and Safety Executive has been informed the incident.