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.

The Canal & River Trust said the path at Pontcysyllte Aqueduct would close between 09:00 GMT and 15:00 from Monday until 17 February.
The towpath will be open outside these hours from Monday to Saturday and will be open all day on Sundays.
Repair work is needed on the parapet of the 126ft (38m) tall structure.
The Canal & River Trust said said: "These measures are to protect the public whilst we undertake these important works, allowing them to be undertaken safely by our operatives."

Three other people in the grey Ford Mondeo, an 82-year-old woman, a 77-year-old woman and a 67-year-old man, were taken to hospital with minor injuries.
The crash happened at 23:00 GMT on Wednesday on Sheffield Road at Hoyland Common.
The 85-year-old was taken to hospital where she later died.
A mother walking her children to school in north Wales is in hospital with serious injuries after being attacked on a busy footpath.
[NEXT_CONCEPT]
Maintenance work on a Wrexham aqueduct means the towpath will be closed for six hours a day.
[NEXT_CONCEPT]
An 85-year-old woman has died after the car she was in crashed into a wall in Barnsley.