Boris Johnson has said he is "shocked" by the stabbings in Manchester, which left four hurt.
Counter-terrorism police are currently investigating the incident which took place at a shopping centre in Manchester.
A man in his 40s has been arrested on suspicion of serious assault, Greater Manchester Police (GMP) revealed.
Three people were stabbed during the incident at Arndale Centre while a fourth was hurt but was not admitted to hospital.
One patient had suffered "serious" injuries, the North West Ambulance Service said.
"Shocked by the incident in Manchester and my thoughts are with the injured and all those affected," Prime Minister Boris Johnson tweeted.
"Thank you to our excellent emergency services who responded and who are now investigating what happened."
A spokesperson for the GMP said: "A 19-year-old woman was taken to hospital with stab wounds. Another woman was also taken to hospital with stab injuries. Both their conditions are described as stable.
"A man in his 50s has also been taken to hospital with stab wounds.
"A fourth victim - a woman in her 40s - who was not stabbed - has been assessed and did not need to go to hospital following assessment by paramedics."
The police also added that they are "keeping an open mind about the motivation of this terrible incident and the circumstances as we know them".