Mr Ellis said he had noticed two officers running up the stairwell in his block of flats in the Gleadless area of the city and then a woman resident emerged.
“She was saying that her boyfriend was in the process of chopping up some coppers and trying to kill them,” he said.
“She said he’d lost his mind, the aliens were chasing him and he was trying to kill the police officers that I’d just seen running up the stairs.”
Mr Ellis said: ” As she did so, the lady police officer, who’s been injured the most, came half-staggering, half-falling out of the stairwell pursued by this big bloke, this bodybuilder, with an axe.
“It was a frenzied attack, chopping at her with the axe. She was on the floor with her baton up, pleading for somebody to help her, to stop him hurting her.”
He said the injured officer shouted: “He’s going to kill me, get him off me.”
Mr Ellis said the man fled through a nearby underpass when her male colleague arrived.
He then described how he tried to lift the officer up by the shoulder but she was so badly injured that he ended up dragging her to his flat by her body armour.
“So she asked me to drag her to my house to get her away,” he said.
“She thought he was going to kill her.
“She said ‘He’s going to finish me off, he’s going to kill me, you’re going to have to get me out of here. Drag me, drag me’. So I dragged her by her body armour with blood pouring out everywhere.”
Mr Ellis said he locked himself and the two women in his flat in Plowright Close until a large number of police arrived.
He said paramedics worked on the officer for more than an hour in his hallway, which is now covered in blood.
Other neighbours said the incident continued when the attacker went into a nearby Co-op store.
South Yorkshire Police said a total of five officers were injured in the incident and a man in his 30s was arrested inside the Co-op on suspicion of attempted murder.
Deputy Chief Constable Dawn Copley said: “This incident serves to remind us all of the dangers our officers face every time they respond to an incident, putting themselves in harm’s way to serve and protect local communities in South Yorkshire.
“The officers who attended in Gleadless last night were faced with an extremely dangerous situation and showed immense bravery dealing with a violent individual. Our thoughts are with those who were injured on duty and full welfare support has been put in place for all officers affected.”
South Yorkshire Police and Crime Commissioner Alan Billings said: “The recent attack on several police officers answering a call in a Sheffield suburb was a very serious incident that should make us all pause. One female police officer taken to hospital and others received medical treatment.
“I understand that a member of the public helped the injured officer.
“There may be times when we criticise the police but, whenever we do so, we should never forget that every day officers are responding to calls never knowing what will confront them. They risk their own safety on a daily basis so that our safety can be assured.”
Dr Billings said: “But we should be in no doubt that we owe police officers a debt of gratitude for what they risk every day in order to maintain law and order and keep our communities safe. If you get the chance, you might want to thank them personally today.”
Mr Ellis said he was only about 20ft (6m) away from the attacker.
“He was chopping bits off her,” he said.
He said: “It was a least half a dozen to eight swings of the axe. He wasn’t holding back at all. It was a full-blooded, frenzied attack with a hatchet.
“He actually was measuring his blows. He even waited for her to move her arms so he could get another chop in.”
Asked what the attacker was saying as he did this, Mr Ellis said: ” He was saying ‘You think you’re going to kill me, do you? You think you’re going to stove my head in?'”
He said he had just returned home at about 8pm on Tuesday when he followed the two officers who were running up the stairwell next to his flat.
He said the attacker, who was a large man, appeared to be the boyfriend of the woman who ran out first.
After the incident, he said, police flooded the area.
Mr Ellis said he lost count after 15 police cars arrived and he counted more than 40 officers.
He said he did not know whether to get involved to begin with but was spurred on when his neighbours said: ” He’s going to kill her if you don’t help her.”
He said: “I had to put this woman’s welfare first because she going to end up getting chopped to pieces if somebody doesn’t help.”
Mr Ellis said the male police officer managed to distract the attacker before he fled, by waving his baton and shouting.
Asked what the officer shouted, he said: “Like you would at a mad bull – which is exactly what he (the attacker) was. Just a complete psycho.”
But Mr Ellis rejected suggestions that he was a hero who saved the woman’s life.
“I’m not having that,” he said.
“If I helped, that’s all I’m bothered about. I’m not being dramatic. I just want to make sure she’s all right.
“Whether I had anything to do with her being saved or it just helped the situation to dissolve itself, it doesn’t matter. The thing is, she’s alive.”
Chief Superintendent David Hartley said the attacker was subdued at the Co-op with a Taser, batons and “other non-lethal force”.
He said armed officers were on their way to the scene at the time of the arrest but were not deployed.
Speaking at the scene, Mr Hartley would not confirm that the man was carried out of the shop on a stretcher but said he did suffer some minor injuries as he was arrested.
He said the woman officer was conscious but was facing surgery later on Thursday.
Mr Hartley said she was single, with no children, and had about 10 years’ service.
The senior officer said all the other injured officers were well enough to be still working on the case on Thursday morning.
Mr Hartley said he had heard reports of t he brave actions of members of the public to help his officers and he hoped to be able to thank them personally later in the day.
He described the initial call as a “r outine response” to a domestic incident but said his officers then faced a ” sustained violent attack” and “extreme violence”.
“Whenever any of our colleagues face that ferocity and level of violence it does send shockwaves,” he said.
“We expect risk, and part of our job is to come between the public and harm. I have enormous respect for the team of officers last night who did just that – n o hesitation at all putting themselves between the public and harm. And showing incredible bravery, bringing a man who was clearly intent on potentially killing someone into custody.”
Mr Hartley told Sky News the badly injured officer had “received some grave injuries” during the “horrific” attack.
“She has a serious injury to her head with a fractured skull, she has a broken leg and she has some really serious injuries to the hand consistent with trying to defend yourself from a man who is attacking you with an axe,” he said.
He added that he had visited her this morning and “she remains in good spirits” despite her injuries.
“She’s got her family and her loved ones around her,” he said. “But in terms of medical treatment that’s going to go on for some time now.”