Almost half of all ambulances here are failing to arrive to the most seriously ill patients within the target time.
It is now nearly a year since the targets were last hit.
Opposition parties have called for 'immediate action' to improve response times, whilst the Welsh Government has admitted the situation as unacceptable.
- The target for 'immediately life-threatening' calls is for 65 percent of ambulances to arrive at the scene within eight minutes
- In March 2013, only 53.3 percent arrived at the scene within eight minutes
The figures for March show that the national target for 65 percent of ambulances to respond to calls for 'immediately life-threatening' cases within eight minutes was missed in every local council area in Wales.
It drops to 42.1 percent in Rhondda Cynon Taf, and 43.5 percent in Merthyr Tydfil.
Ambulances arrived within eight minutes for Pembrokeshire, Wrexham, Conwy and Denbighshire between 60 and 65 percent of the time.
The Welsh Conservatives have called for "immediate action" from the Welsh Government to address how failings over ambulance response times.
– Darren Millar, Shadow Health Minister
Response times have slumped to a shockingly low level and we need an urgent explanation.
Only half of life-threatening calls received a timely response in March and that means inevitable distress for thousands of patients.
Every minute lost can harm a patient’s recovery chances and delays can lead to death.
The closure of local services is only adding to the pressure on staff and it’s vital that unwanted NHS reorganisation is properly considered in the current ambulance service review.
Frontline staff must be put first and our health service must receive the investment it needs.
The Welsh Liberal Democrats have described the Welsh Government's failure to address ambulance response times as "an absolute disgrace".
They have highlighted how targets here in Wales are already 10 percent behind England and Scotland, but are still not being met.
– KIRSTY WILLIAMS, WELSH LIBERAL DEMOCRAT LEADER
I recognise that there were a large amount of calls in March with difficult weather conditions, but there really is no excuse for these appalling figures.
Fast ambulance response times often mean the difference between life and death.
Welsh Ambulance staff are working incredibly hard, but they are clearly working in a failing system that is getting in the way of them doing their job.
The Health Minister announced yesterday that the Ambulance Review is expected to be published next month - the ninth review in six years. This must be the final one, lives are on the line here and we need results.
Plaid Cymru says the figures showing a tenth successive month where ambulances failed to meet their response-time targets highlights that the NHS "is at crisis point."
– ELIN JONES, PLAID CYMRU SHADOW HEALTH MINISTER
It begs the question how much further the situation can deteriorate before it collapses. It is clear that the NHS is struggling to cope with the enormous pressure that it is under.
We need to stop this trend but worryingly, the Welsh Government’s plans to centralise hospital services will put even greater pressure on fewer A&E departments.
A Plaid Cymru government would also extend out of hours services so people have alternatives to A&E departments, and we would make sure that the ambulance service to be properly equipped to meet the challenges it faces.
The Welsh Government commissioned a review into the Welsh Ambulance Service last November.
The Health Minister now has the findings of that review, which will debated in the Senedd on 7 May.
A Welsh Government spokesperson said: "The Health Minister Mark Drakeford is aware of the pressures on unscheduled care and the impact this is having on emergency ambulance performance."
"During his statement in the Senedd yesterday, he outlined short, mid and long-term plans to tackle the matter, which includes implementing immediate actions to reduce ambulance handover times at A&E departments."