Forensic officers have cordoned of a house and the entrance to a park after a young man was stabbed.
Three people, two men and a woman, were arrested at the scene on Davidson Road in Old Swan, as the victim was rushed to hospital.
The incident happened shortly after 3pm on Friday and police are likely to remain in the area throughout the evening.
Road closures were put in place as police and forensic officers launched an investigation into the attack.
Just minutes after emergency services were called to the scene, an air ambulance landed at nearby Rathbone Park which has now been closed off.
The man, in his 20s, was taken for treatment and is believed to have sustained serious injuries.
Yellow evidence markers have now been laid on a footpath close to the scene as forensic officers were seen carrying clear evidence bags from their van into a house.
The three people arrested will now be questioned by officers on suspicion of Section 18 wounding with intent.
In a statement, a spokesperson for Merseyside Police said: "Detectives have arrested three people and are appealing for information following a stabbing in Old Swan this afternoon, Friday 12 February.
"At around 3.10pm, emergency services were called to Davidson Road to reports of a man in his 20s being assaulted. The victim was taken to hospital via ambulance for assessment of serious injuries.
"Two men and one woman were arrested a short time later on suspicion of Section 18 wounding with intent. They have all been taken to police stations for questioning.
"Officers remain in the area to carry out forensic, house-to-house and witness enquiries."
Detective Inspector Jennie Beck said: "Although we have arrested three men in connection with this serious assault, we're keen to speak to anyone who saw or heard anything suspicious in the area this afternoon.
"Your information, home CCTV, dashcam or other images could be vital as we continue to investigate.
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"We take positive action on all you tell us, so speak directly or anonymously and we'll do the rest."
You can contact police social media desk on Twitter @MerPolCC or Facebook ‘Merseyside Police Contact Centre’ with reference 511 of Friday 12 February, or call 101.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111 or via their online form at: https://crimestoppers-uk.org/give-information/give-information.
