Paramedics found the woman inside Hotel CBD, with a stab wound to her back.
Her condition was described as "not life-threatening".
The hotel, on the corner of York and King St, remains in lockdown.
Emergency services are still working through the scene and are unable to confirm whether more were injured in the man's stabbing rampage.
NSW Police Superintendent Gavin Wood told reporters there were a "number of attempted stabbings by the same offender".
"Bearing in mind we have multiple crime scenes and we are in the infancy stage of this investigation," he said.
"It is a serious and significant investigation that I want to put out there but I also want to put out there most importantly, the threat has been negated."
A man who was involved in the alleged offender's arrest suggested more people had been stabbed.
"You f**king piece of s**t, do you know how many people you just stabbed you dog?" the man said in a video taken by 7 News reporter Andrew Denney.
When questioned by fire fighters as they pinned the man down, the witness was asked what he'd seen happen.
"He just stabbed a chick in broad daylight. He stabbed a chick, came running down and he just stabbed people," he said.
Right before his arrest, the man was filmed jumping onto cars on the corner of King and Clarence Street and screaming out.
"Shoot me, shoot me in the f**king head, I've got a f**king gun," the man was filmed saying in the street.
Emergency services rushed to the CBD around 2pm this afternoon following reports the man was walking along York St, Sydney, armed with a knife.
