A greater number of ambulances in Wales are missing targets for reaching the most serious incidents within eight minutes, according to official figures.
Fewer ambulances are reaching the eight-minute target
Between July and September, 54% made the eight-minute target - a fall from 57% recorded in the previous quarter.
The Welsh Assembly Government wants 60% of ambulances to reach life-threatening cases in eight minutes - itself a reduction on a previous 75% target.
The assembly government said the latest figures were "not good enough".
The statistics, provided by the NHS, cover the 76,000 emergency calls made in the period from 1 July to 30 September.
According to the figures, 80.5% of responses to all emergency calls arrived within target times, but in life-threatening Category A cases, just 54.2% achieved the eight-minute target.
The assembly government said the Welsh Ambulance Service was experiencing "unprecedented demand" but said it was committed to extra funding for improvements.
A statement read: "The present levels of performance are not good enough. This is why root and branch modernisation is needed.
"We have given our commitment to provide extra funding to the ambulance trust but this will need to be phased in over a number of years and be backed by a clear modernisation plan."
Opposition parties criticised the fall in the percentage of ambulances reaching their target response times.
Welsh Conservative health spokesman, Jonathan Morgan, said: "The fact that they are now at their lowest level since the advent of devolution should serve as a wake-up call to the health minister and his Labour colleagues.
"It cannot be right that many people who require urgent medical treatment are not seeing the ambulance they called turn up on time."
Plaid Cymru health spokesperson, Helen Mary Jones, added: "These official figures are further proof that Plaid was correct to secure an inquiry into ambulance services in Wales.
"I look forward to seeing the report of the inquiry team."