The incident took place close to Caernarfon's Crown Court and fire station just before 09:00 BST on Thursday.
The mother-of-five was airlifted to hospital in Stoke-on-Trent.
North Wales Police has said her 46-year-old partner has been arrested.
"This is being treated as a domestic-related crime but I would like to reassure the community that a swift arrest was made," said Det Chf Insp Iestyn Davies.
The Welsh Ambulance Service said they were called at 09:00 BST to reports that a woman had been assaulted.
Police said the victim remains in a serious but stable condition.
Forensic investigations are being carried out at the location, which links nearby estates to a local primary and secondary school.
A mother walking her children to school in north Wales is in hospital with serious injuries after being attacked on a busy footpath.