Detective Sergeant Colin Welsh said police located two injured people about 2am today in a vehicle in William St, after attending a separate incident in the street.
Both were seriously hurt and transported to hospital by officers.
A third seriously injured person also went to hospital.
Det Welsh said initial indications suggest those involved were known to each other and police were not seeking anyone further at this stage.
"Police would like to speak to anyone who was in the area at the time, or who may have information which can assist our investigations."
He urged anyone with information to call 111 and quote file number: 240526/1036.
Information could also be reported to police anonymously by phoning Crimestoppers on 0800 555 111.
