Ambulance staff say it is common to see up to five ambulances queued at the Canberra Hospital during peak periods, as they wait to offload patients to hospital beds.

There is a minimum of eight ambulances operating in the territory at any one time.

An agreement between the ACT Ambulance Services and ACT Health states that patients are expected to be offloaded into a hospital bed 20 minutes after triage.

Official data from ACTAS electronic patient care records shows 90 per cent of the 16,000 patients transported to the hospital since July 2011 were removed from ambulances within that timeframe.

It took between 20 and 40 minutes to offload 1440 patients, and over 40 minutes to offload 160 patients.

But one paramedic, speaking to The Canberra Times anonymously, said that data hid the scale of the problem. He said although patients were removed from the ambulance, they were spending significant periods lying in hospital corridors or waiting areas, supervised by ambulance or nursing staff.

''It's not uncommon to arrive at Canberra Hospital and expect a delay,'' he said. ''Sometimes you are kept for more than double the time we are expected to clear. That can be up to 40 minutes or longer.

''When we're kept waiting longer than 20 minutes with a patient on an ambulance stretcher, that's going to delay our ability to respond should calls come in, particularly when we have multiple ambulances at Canberra Hospital waiting to be offloaded.''

Transport Workers Union official Ben Sweaney said the ACT dealt with bed block better than most other jurisdictions. But delays had a greater impact on the ACT Ambulance Service, because of its relatively low number of ambulances.

''Even though we're doing it well, we don't have enough resources,'' Mr Sweaney said.

''You notice it especially on those big nights, the Fridays or Saturdays … the days when people drink, and you always run the chance of going below minimum crewing. You get a case or two cases where people have got to wait at the hospital for a little bit longer, you will be tasked with a fire crew for 20 minutes before you can send an ambulance.''

An ACT Health spokesman said the delays at the hospital were minimised by ACTAS' offload policy.

That policy sees paramedics hand patients over to hospital staff, and kept in waiting rooms, treatment spaces or hospital corridors, when necessary. ''At times of high activity with many ambulances presenting at the same time, patients may be offloaded to a trolley in the corridor in line with the ACT Ambulance Service offload policy, until a treatment space is made available,'' the spokesman said.

Often, when multiple ambulances are caught in bed block, one crew will be left behind to supervise multiple patients, allowing the other crews to get back onto the road. An ACTAS spokesman said the problem of bed block at the hospital was not hindering the operations of the service. The computer aided dispatch system ensured that the closest and most appropriate ambulance was sent to each emergency call.

ACT Health and ACTAS were working together to ''maximise the availability of ambulance resources''.