NSW Health Minister Jillian Skinner has instructed NSW Ambulance and the Ministry of Health to review the response categories, after Fairfax Media revealed that a number of previously category one emergency "lights and sirens" ambulance responses had been shifted to a less serious category that only requires an ambulance to be assigned when one is available and to drive without emergency signals.

Resource shortages within the ambulance sector mean in some cases paramedics will not arrive for half an hour or more, as the service is already struggling to meet demand for the category one cases. A number of recent scandals linked to long wait times for ambulances have involved 2I or lower priority cases - but NSW Ambulance says it has no choice but to prioritise patients judged to have life-threatening conditions.

Sources have told Fairfax Media that the downgrading of many of the less serious cases was appropriate, but a lack of available cars to assign to them is potentially dangerous.

Women's Electoral Lobby chair Melanie Fernandez​ said her group held deep concerns about the change to the classification of serious haemorrhage after sexual assault.

"It's unacceptable for a government that says it's committed to addressing domestic violence … it's dangerous," she said. "I do understand things need to be prioritised ... but serious haemorrhage after sexual assault is too great a risk, particularly with waiting times at the moment meaning it's often not going to mean a matter of minutes."

As well as serious bleeding after rape or suicide attempts, haemorrhage after assault or during the second trimester of pregnancy has also been moved to 2I, or category two, immediate response required.

The ambulance service keeps no performance data on how long it takes to reach these patients, and cases no longer contribute to assessments of response times.

Health Services Union councillor and intensive care paramedic Greg Bruce​ said there could be 20 or 30 cases at a time waiting with no vehicle available.

"It is clear that they are waiting for outside of the length of time they should be waiting, but the problem is there are no clear reporting targets or KPIs for it, so we don't know what the actual data is," he said.

HSU secretary Gerard Hayes said not all jobs should be category one and paramedics wanted cases prioritised.

"The problem in Sydney and NSW is that during peak times of the day there are not enough ambulances to cover category 1 cases," he said.   "This leads to 2I patients, who should have an ambulance dispatched immediately, waiting in the queue for an hour.

"If the government prioritises a job as serious enough to require an ambulance be dispatched immediately, the public can expect the government to resource NSW Ambulance enough to ensure that happens."

A spokesman for NSW Ambulance said the 2I category represented "potentially serious" cases such as abdominal pain that did not have any emergency symptoms.

"NSW Ambulance paramedics attending non-medical emergencies could mean a patient with a life threatening emergency may have to wait, potentially putting their life at risk," he said. "At times it means those with lower acuity conditions will wait longer for a paramedic to arrive or instead be referred to another health pathway."

He said NSW Ambulance was conducting a campaign, "Is this an urgency or is this an emergency?", to ensure people knew more about the right services to call.

Mrs Skinner told State Parliament on Tuesday afternoon that the categories were used internationally, but she believed they should be reviewed and NSW should lead the way.

"I do not believe that people suffering these conditions should wait," she said. "I have asked Ambulance and the Ministry of Health to take a look at [this issue]".

However, she also said she was "disappointed" by "scaremongering" from the HSU about ambulance resourcing.

NSW Opposition Leader Luke Foley said: "Another day and yet another example of an ambulance service in crisis thanks to the Baird government's callous mismanagement.

"The Baird government must acknowledge the evidence of bed block and lengthy queues of ambulances in emergency departments are affecting patient safety."

The Emergency Hierarchy

Category One - must arrive within 10 minutes, lights and sirens used.

• 1A is the most serious classification and can be described as imminently threatening life. For example where a person is drowning, choking, in cardiac arrest, hanging or shooting.
• 1B is the next most serious classification and can be described as potentially threatening life. For example where a person is perhaps not fully alert or has impaired consciousness.
• 1C is a patient who is alert and conscious and can be described as the third most serious type of case. For example where a person has chest pain or abdominal pain.

Category two - no performance data on wait times, normal driving conditions

• 2I - Immediate response required, car assigned if no category one takes priority. Cases include abnormal breathing, speech problems, some cases of serious haemorrhage and early pregnancy loss. 

(Source: NSW Ambulance. For more info visit "Is your urgency an emergency?")