Young children are said to be among at least eight people stabbed in scenes one witness described as like a “horror movie”.
Armed police arrested a man and seized a knife after being called to the “major incident” at a property on Hart Street, in Southport, north of Liverpool, at about 11.50am on Monday.
North West Ambulance Service (NWAS) said it had so far treated eight patients with stab injuries, who have been taken to Alder Hey Children’s Hospital, Aintree University Hospital and Southport and Formby hospital.
Prime Minister Sir Keir Starmer said the incident was “horrendous and deeply shocking”.
Home Secretary Yvette Cooper said she was “deeply concerned”, as Alder Hey declared a major incident and asked parents not to bring their children to the emergency department unless it was urgent.
Colin Parry, owner of Masters Vehicle Body Repairs on Hart Street, who called the police, said he believed six or seven “young girls” had been stabbed.
He told the PA news agency: “The mothers are coming here now and screaming.
“It is like a scene from a horror movie.”
“Police have got him,” he added.
“It’s like something from America, not like sunny Southport.”
A local parent, who did not wish to be named, said his daughter was “traumatised” by the attack.
He said: “My daughter was in it and she was traumatised.
“She ran away and she’s safe.”
Merseyside Police said: “There are a number of reported casualties and more details will be confirmed when possible.
“Armed police have detained a male and seized a knife. He has been taken to a police station.
“Please avoid the area while we deal with this incident. There is no wider threat to the public.”
In a post on X, formerly Twitter, Sir Keir said: “Horrendous and deeply shocking news emerging from Southport. My thoughts are with all those affected.
“I would like to thank the police and emergency services for their swift response.
“I am being kept updated as the situation develops.”
Ms Cooper posted on X: “I am deeply concerned at the very serious incident in Southport. All my thoughts are with the families and loved ones of those affected.
“I have spoken to the Merseyside Police and Crime Commissioner to convey full support to the police & thanks to the emergency services responding.”
Southport MP Patrick Hurley said he was “deeply concerned” by the reports.
In a statement on X, formerly Twitter, he said: “I am deeply concerned by the reports coming from Merseyside Police about a major incident on Hart Street in Southport today.
“I am hoping for the best possible outcomes to the casualties affected.”
NWAS said it had dispatched 13 ambulances along with specialised resources of its Hazardous Area Response Team (Hart), an air ambulance and doctors.
It said: “We’re assessing the situation and working with emergency partners.”
Alder Hey Children’s Hospital said: “We can confirm that the trust has declared a major incident.
“The trust is working with other emergency services to respond to this incident and our emergency department is currently extremely busy.
“We ask parents to only bring their children to the emergency department if it is urgent.
“All other appointments and services are running as normal.”