People have reacted in disbelief to the shocking violence shown in a video shared widely on social media.
The sickening video, shows a fight which is believed to have broken out in Williamson Square in Liverpool city centre this weekend.
Merseyside Police said the incident has not yet been reported to them but they are aware of the footage circulating online and urged anyone with information to come forward.
In the video, two men can be seen fighting on the floor as two others who are standing over them, throw kicks and punches towards them.
One man then puts his hand in his pocket and pulls out what appears to be a weapon, before moving his arm in three short sharp thrusts towards a man lying on the floor.
Following the story, people have taken to the ECHO's Facebook page and website to share their disgust at the violence, and also to criticise the people who 'stood around and laughed' while one man appears to be stabbed repeatedly.
On Facebook, Tracy Gibbs-Bullen said: "Absolutely disgusting - someone's child that and using a weapon nothing tough about that.
"And to film it, why would you do that? Hope they are ok".
John Corlett posted: "The behaviour is disgusting - I mean the people who stood there videoing it. They could have helped, what a sick bunch as bad as the two assailants."
Karen Armstrong agreed, commenting: "How sad that the divvie getting it on his phone thought the whole thing was quite amusing."
Gwenda Anne asked: "Why didn’t the two men who actually look like security help[?] They just casually walked over after event."
On the ECHO website, Scouse8uy posted: "Someone could have easily stopped those two ‘young’ kids attacking the defenceless guy. I mean how old do they look???"
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Some people defended the actions of those filming the attack, saying to intervene would have put their own safety at risk.
Erin Anais said: "Everyone saying why didn’t the person filing do anything. I certainly wouldn’t be getting involved in a stabbing and putting my life at risk if I had my phone I’d do the same get video evidence."
While Henry Moffat posted: "At least filming it means there’s a chance they will be caught."
Police have increased patrols today to help prevent any further incidents and ensure people can enjoy the city centre safely.
Enquiries are ongoing to establish the full circumstances, including when the incident occurred.
Chief Inspector Gary O’Rourke said: “If you saw this shocking incident – if it was you filming the video, you are the victim or you witnessed anything then please tell us.
Whether you come forward directly or anonymously, your information could be vital to help bring those responsible to justice.
“Knife crime has no place whatsoever in our communities and we rely on members of the public coming forward with information about such incidents to keep our streets safer.
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“We are increasing patrols around the city centre today to make sure that everyone can enjoy themselves safely while out and about.
“As a force we have seen a decrease in reports of knife crime over the past two years.
"However, over this last week we have seen some unacceptable and criminal acts of violence in the City Centre including two appalling hate crimes.
"We will continue to work tirelessly with the public and our partners to prevent violence and remove the scourge of knife crime from our streets.
“Reducing knife crime is one of our force priorities and our message to those who might think about carrying a knife is clear: It is just not worth the risk.
"Every day we are out on patrols, conducting stop searches, executing warrants, putting every effort into arresting offenders and putting them before the courts.
“We regularly search land and homes where we believe knives have been stored and if you involve yourself in knife crime, it is only a matter of time before you end up hurt or arrested.
“We are also working closely with our communities, schools and safeguarding partners to tackle knife crime by taking a more preventative approach, working to educate, divert and influence young people away from knives and other violent crimes.
"During Operation Sceptre, a dedicated week of action to tackle knife crime, police officers proactively engaged with young people to warn them about the dangers of carrying a knife and what this sort of criminal activity can lead to.
“We will never stand by and allow people to carry knives and threaten the safety of themselves and others.
"With the public’s help, we can make Merseyside a safer place and I appeal to anyone who has any information in relation to this incident, or knife crime in Merseyside to contact police.”
Anyone with any information about knife crime in Merseyside, or who has any information on the incident in Williamson Square and other violent incidents being investigated in the City this week are asked to contact police via their social media desk via Twitter @MerPolCC or Facebook ‘Merseyside Police Contact Centre’ with reference 414 of 13/06.
You can also contact the independent charity Crimestoppers anonymously, on 0800 555 111 or via their online form here.