Police have described scenes of fear and anxiety at a Dunedin party where a young woman died on Saturday night.

Emergency service were called to Dundas St at around midnight to help break up the event.

By the time they arrived one woman had sustained fatal injuries and another two were seriously injured. Witnesses say they may have been trapped and trampled during a pile-up on the property's stairs.

Otago Coastal Area Commander Marty Gray says police arrived to reports of people being injured as they tried to leave the party.

"When our officers arrived there was, as you can probably visualise, 500-600 party-goers," he told media on Sunday afternoon.

"A lot of them anxious, a lot of them trying to get out of the premises, a lot of them trying to get into the premises, a lot of disorganisation and a lot of uncertainty, a lot of anxiety."

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A witness told Newshub the house was "incredibly crowded" and the victim was brought out in a terrible state.

"The girl, I'm presuming is the one who passed away, she was carried out by four people and outside the front of the house, they were probably doing CPR on her for about 15 minutes before taking her onto an ambulance.

"Seeing her being wheeled away, I could see the heart rate monitor and it was just a flat line so that was pretty awful to see."

Tributes to the victims are being left outside the scene. Commander Gray says police have offered support to the family.

"It's news no parent wants to hear. They live outside of Dunedin and they've been told of their daughter's death this morning," he says.

"Just like a parent myself, just join with us and understand the situation those parents [of the deceased] are going through."

Police say it's too early to say if charges will be laid, and ask any attendees who have not spoken to officers to get in touch.

"If you were at the party and have not spoken to police, we would ask you to please get in touch, to help us piece together what happened," Commander Gray says.

Victim Support is available for those who were present at the event.