Two people have been treated for stab wounds after an incident at a college campus, the ambulance service said.
They are described as stable in hospital after the attack in Belfast.
The incident happened at Belfast Metropolitan College's Millfield campus, close to the city centre.
The ambulance service confirmed that two people had suffered stab wounds.
A Police Service of Northern Ireland (PSNI) statement said: " Police remain at the scene of a stabbing incident at college premises in the Millfield area of Belfast.
"One male is currently in hospital in a critical condition whilst another male who was detained at the scene is also being treated in hospital for non-life threatening injuries. There are no further details at present."
The Northern Ireland Ambulance Service said the men were taken to the Royal Victoria and Mater hospitals in Belfast.
A spokeswoman for Belfast Met said: "There has been a security incident at the Millfield campus. Emergency services are involved."
A hospital spokeswoman said: "We are describing them both as stable."