It is believed one man may have been seriously assaulted and was later transferred to Letterkenny General Hospital.
The incident took place in the McNeely Villas area.
Gardai had the area cordoned off and a number of examinations were being undertaken.
Officers were remaining tight-lipped about the assault.
Meanwhile a man is being treated in the Intensive Care Unit of Letterkenny General Hospital after an incident in the town overnight.
It is unclear at this stage if the man in ICU is the man involved in the incident at McNeely Villas.