An 18-year-old student has been taken to hospital after she suffered knife wounds to her face, near Bury College.
A college statement said the incident took place in an underpass in Bury town centre and college staff went to help the injured woman immediately.
Greater Manchester Police said officers were called to the "serious" attack at 1450 BST. The woman was taken to Fairfield Hospital.
Another girl, 16, who is not a student at the college, has been arrested.
Police were called to the Woodbury Centre on Market Street, following the reports of an assault.
One mother, who had just dropped her son off at the college and saw six police cars and two ambulances outside, said: "At first, I thought it was some sort of emergency drill. So I pulled over and sent my son a text. He said he was OK but that it looked like somebody had been stabbed.
"It's very worrying. As a parent, you want to know that your child is safe.
"As far as I'm concerned, it's a brilliant college. The security is great, everyone has got security passes to get in and out and they check them regularly. But when it's on your own doorstep, it does make you nervous, to be honest."