The news comes as figures show ambulance shifts fell below minimum staffing levels more than 40 per cent of the time in the last financial year, despite crews working almost 36,000 hours of overtime.

The boy's family also found themselves without an ambulance for their young daughter in 2012, when she was spiking a dangerously high fever. On both occasions, the children's father said he was told an ambulance was on its way, only to get a call back saying that crew had been diverted to another call.

He was advised to take his child to hospital himself, which he did, in a "mad, stressful" rush.

"I'm worried some kid's going to die because they can't get an ambulance," said the Charnwood man, who did not wish to be named.

"I don't live in a third world country, when you call an ambulance for your kid, you expect it to turn up."

While ESA confirmed both incidents to Fairfax Media, quality and patient safety officer at the ACT Ambulance Service Megan Davis said the November case was unusual.

"We were inundated with calls that night, a lot of them life-threatening," Ms Davis said.

"Any child we will always try to get an ambulance to."

She said life-threatening calls were given first priority, and in this case the boy was deemed to be stable enough to wait, but people were normally not told to make their own way to hospital.

On each shift, a clinician will triage calls that are "not immediately life-threatening" and check on patients still waiting for ambulances, Ms Davis said.

A review into both cases was undertaken and standard procedure had been followed, she said.

ACT Emergency Services Minister Mick Gentleman said that, despite growing demand, the ACT had the best ambulance response times in the country as well as highest levels of patient satisfaction.

Recruitment was currently underway for 11 new paramedics, with 25 more also coming on board later this year.

But shadow minister for emergency services Giulia Jones said the government had created a workforce reliant on overtime, "leaving the Canberra community [and ambulance workers] vulnerable".

"It's scary to think how much worse [this could be] if our workers weren't able or willing to put in this additional overtime which really cannot be demanded of people after working a 10- or a 14-hour shift," Ms Jones said.

"This is not good management and it is putting our ambulance workers under further stress."

Earlier this month, Mr Gentleman announced a review of the minimum staffing guidelines for ambulance workers, as the measure did not appear to be an "accurate reflection" of the staff actually required.

"Advice to me from the ACT Ambulance Service is that during periods of low demand - for example night shifts during the middle of the working week - ACTAS can operate effectively with fewer than 10 crew," Mr Gentleman said.

While overtime "plays a key role in operating any 24/7 emergency service", he said a new welfare manager had come on board with the ESA this month to develop a peer support program.

The minister assured the community they could have "the highest confidence" in the performance of their ambulance service, and thanked paramedics for their work.