The UK ambulance service said that it was treating four people after the incident at the Arndale shopping centre in Manchester.
Five people have been stabbed at shopping centre, and counter-terrorism police are leading the investigation, British police said in a statement.
"We are on the scene, we are treating four patients," a spokeswoman at the North West Ambulance Service said.
Manchester Police said on twitter that they were responding to an incident at the shopping mall.
According to media reports, armed police officers are patrolling inside the shopping mall.
UK police said that a man has been arrested on suspicion of serious assault over the incident at the shopping centre.
"A man in his 40s has been arrested on suspicion of serious assault. He has been taken to custody for questioning," police said.
Footage from outside the shopping centre, shared on social media, shows police vehicles arriving at the scene.
It is not known whether there are any fatalities.
According to recent data from the Bureau of National Statistics, the number of knife crimes in England and Wales is growing steadily. For the year from March 2018 to March 2019, the police registered more than 43,500 crimes with the use of knives and other piercing and cutting objects, which is 8% higher than the previous year.