Ambulance Victoria says a call about a drowning child was mistakenly made a lower priority, as the family calls for improvements to response times.

The family of a toddler who drowned in the bath wants faster ambulance response times, but Ambulance Victoria can't promise they will improve.

Ambulance Victoria says the call about a drowning child was mistakenly put at a lower priority than it should have been, so the nearest ambulance wasn't sent immediately.

Emmy Boyle was nearly four when she died last month after her mother briefly left her in the bath to get a towel.

"The best thing we can do moving forward is to ensure that no other families have to wait the time we waited for assistance," Pauline Boyle told reporters on Tuesday.

An ambulance was originally sent from 12km away after the emergency call-taker did not give the case the highest priority.

Another ambulance was sent from 8km away once the mistake was realised, and it arrived 21 minutes after the call was first made.

Emmy's father Rohan Boyle said Victoria's ambulance response times had gone backwards.

"The system did work eight years ago. They had eight-minute response times," Mr Boyle said.

Ambulance Victoria general manager Tony Walker could not promise response times would improve with his current resources, but said paramedics were working to free up more vehicles.

"Our plan is about trying to improve ambulance response times by moving patients away from the emergency sector that don't need ambulance response," Mr Walker told reporters.

He said the last 12 months' performance data showed response times had improved.

The ambulance crew that did get to the Boyles' Gowanbrae home took 17 minutes to drive 8km during peak-hour traffic.

Mrs Boyle said she was in the bathroom with Emmy but ran downstairs briefly to get her towel.

She found the toddler lying facing upwards in the bath under the water, immediately pulling her out and flagging down her neighbour for help.

Mrs Boyle and her neighbour, a fireman of 25 years experience, called an ambulance and tried to revive Emmy, but they and the firefighters and paramedics who arrived were unable to save her.

A Victorian auditor-general's report tabled in parliament on Tuesday found the Emergency Services Telecommunications Authority (ESTA) has failed to meet its ambulance dispatch standards three years in a row due to staffing and procedural issues.

It also found ESTA's computer dispatch system was old and recent failures had hurt response times.

Premier Denis Napthine told parliament Emmy's case - and the roles of Ambulance Victoria and ESTA in it - would be investigated.

Opposition Leader Daniel Andrews said ambulance response times are the worst they've been and the government needed to accept there was a crisis.

"To be just 14 minutes from the CBD and have to wait 23 minutes for an ambulance is not good enough, it's unacceptable," he told reporters.

HOW EMERGENCY SERVICES RESPONDED TO A DROWNING CHILD:
* Initial triple-zero call 4.40pm; dropped out before details fully taken
* ESTA tried three times to call back; couldn't get through
* Second call 4.42pm; Caller said qualified person giving CPR; Case rated priority one; Ambulance dispatched from 12km away
* Case re-rated priority zero 4.46pm; closer ambulance 8km away dispatched then MFB firefighters
* Firefighters arrive 4.57pm, eight minutes after dispatch
* Ambulance arrive 17 minutes after dispatch.

(Source: Ambulance Victoria and ESTA) Copyright AAP 2014