A student who attended the party told the Herald of "hectic" scenes where intoxicated people frantically tried to exit the flat.
"People were jumping off the top of the stairs onto other people. It was basically a human dog pile. People were mounting on top of each other," she said.
"There was major anxiety, everybody was trying to get out while others were coming in, it was a big wall. People were getting squashed."
Crestani, who had an identical twin, moved from Wellington where she grew up to study at the University of Otago.
Plenty of other partygoers had sustained injuries but fled the scene after they exited the flat, she said.
The student didn't think the flat was big enough to house 600 people at one time but thought hundreds had been through its doors over the night.
Another student told the Herald he left the party early over fears he would get crushed, having watched a documentary on the Hillsborough disaster recently.
"There was one point where I was swept over and fell down with a couple of other people," he said.
"It was pretty standard [for flats to be full], it's happened before at flat parties but this was certainly worse than I've experienced in the past.
"It was like a school of fish moving around … you didn't really have control over what was happening."