The witness had seen a group of "big guys" enter the club about 3am, shortly before the fight broke out.
After spending about half an hour in hiding, she saw about 10 men handcuffed by police and on the floor.
"There was blood everywhere and the guy was on the ground," she said.
"He had multiple cuts and his T-shirt was soaked with blood and there were cuts on his legs and stuff."
Detective Senior Sergeant Nina Pedersen said police were investigating the stabbing at the Quay St venue.
"Police were called in the early hours of Sunday morning following reports that a man had been stabbed," Pedersen said.
"A 25-year-old man suffered a number of stab wounds and was transported to Auckland City Hospital, where he is in a stable condition."
Enquiries were still ongoing at this stage, Pedersen said.
"Anyone with information relating to this incident are asked to call Auckland City Police on 09 302 6557 or Crimestoppers anonymously on 0800 555 111."
St John spokeswoman Beverley Tse told the Herald they received a call about the incident at 3.21am on Sunday.
One ambulance crew transported the man to Auckland Hospital in a serious condition, she said.
The owner of Aura Club declined to comment when contacted by the Herald.