NSW union and Labor figures say the state's ambulance service is so short-staffed that a handful of regional stations are sometimes manned solely by interns.
Emergency Medical Services Protection Association NSW (EMSPA) president Wayne Flint has told AAP he is aware of at least five stations that are reliant on interns with less than three years' experience at critical times like weekend nights.
In one case, Mr Flint claims, an intern was made acting station manager, and in another a woman with just over 12 months' training was stationed in an isolated inland part of northern NSW and left to respond to emergency calls solo.
"We believe this is a trend in regional areas," he told AAP on Friday.
"Some of them may have only just gone through their first year as a trainee."
But the NSW Ambulance Service has moved to reassure the public that interns are well-trained and capable of handling emergencies without more senior colleagues at their side.
"Paramedic interns are not trainees," a spokeswoman said.
"The term 'paramedic intern' is used to describe an employee who has successfully completed the initial phase of training and are certified to work on-road."
The EMSPA's Mr Flint said he was alarmed by moves at one established ambulance station, Nyngan, which serves Bogan Shire in central NSW, to bring in volunteers.
Supplementing an established service with volunteers was a "backward step" that could only be explained by funding inadequacies or mismanagement, he said.
"If ambulance resources for NSW are adequate, then the need for volunteers must identify that there could be a problem with the management of those resources," Mr Flint said.
NSW Labor spokesman Andrew McDonald said government belt-tightening was to blame.
"The ambulance budget went up by two per cent last year and demand by about three times that," he told AAP.
"Something's got to give."
While the paramedics' union says shortages largely affect regional NSW, Fairfax Media reports that highly-trained intensive care paramedics are also absent from Sydney city streets on busy weekend nights.
Fairfax said that no intensive-care paramedics were stationed in inner Sydney on Friday, December 20, after five were unable to work a scheduled shift due to illness.
The closest available unit was reportedly at Rockdale.