The Arndale Centre in Manchester has been evacuated amid reports that a number of people have been stabbed.
Witnesses described scenes of chaos as a large number of police and emergency services descended on the area in the centre of Manchester just before lunchtime.
One video posted on social media showed officers deploying a Taser to detain a suspect who was laid face down on the ground.
Sources have confirmed that there have been a number of stabbings but it is not clear if there are any fatalities.
In a Tweet, Greater Manchester Police said they were responding to an incident in the City centre and would provide further details shortly.
Eyewitnesses reported that the stabbings had taken place in the Starbucks coffee shop inside the Arndale centre.
In a statement a Greater Manchester Police spokesman said: We are currently responding to an incident at the Arndale Shopping Centre in Manchester City Centre. Officers are in attendance and early enquiries suggest that several people have been stabbed.
A man in his 40s has been arrested on suspicion of serious assault. He has been taken to custody for questioning.
One report suggested there were two knifemen, who were attacking people at random.
Paramedics were seen entering the Arndale carrying stretchers.