A 30-year-old mother of four children was on a life-support machine in a Cork city hospital last night after a shooting in the Wellington Road area of the city.
The woman was understood to have been a passenger in a van when she was shot in the head.
Her identity had not been revealed last night.
Gardai in Cork have appealed for witnesses to the incident, which occurred some time after 1 a.m.
Garda sources say that after the shooting she was driven to the Mercy Hospital in Cork, where she received immediate attention.
It is understood that Garda divers will drag the stretch of the Lee near the hospital today in an attempt to recover the weapon used in the shooting. This operation was to have begun last night but, because of tidal conditions, was deferred.
A man is being questioned under Section 30 of the Offences Against the State Act at Mayfield Garda station in Cork.
Meanwhile a forensic examination of the van in which the woman was travelling when she was shot was being carried out at Togher Garda station.