Family members will only be allowed to accompany loved ones in ambulances in "exceptional circumstances" during the nation's Covid-19 response.
St John has announced the change around emergency ambulance transportation of patients today in a bid to "limit the spread of Covid-19 and to keep patient families and health workers safe".
Ambulance officers across the country have been informed of the change.
"While St John understands that patients often like to have a support person accompany them on the ambulance journey, it is necessary to limit the number of people in emergency departments during the current Covid-19 pandemic response," St John Medical Director Dr Tony Smith said in a statement.
"We understand that this initiative may be distressing for patients and families in an already stressful situation but appreciate the public's help with keeping everyone safe."
St John reassured that there would be some exceptions on compassionate grounds such as a patient being gravely ill or when a child is being transported. In such cases, only one family member would be permitted to travel, however.
Last week, St John announced plans to step up ambulance services, including calling in paramedic trainees.
St John director of operations Daniel Ohs said St John had anticipated a need for greater numbers of people able to work on the frontline.
That included finding space in its workforce - paid and volunteer - for "surge capacity". This would see an increase the numbers of fully-trained staff able to work and interact with patients.
Ohs said doing so included the prospect of bringing in staff not needed for other duties - ambulance officers assigned to events now cancelled - or having volunteer St John staff team up with specialist paramedics to free up resources.