Patients waited more than two hours to be admitted to the Royal Glamorgan Hospital as emergencies "overwhelmed' the hospital over the last three days.
Up to seven ambulances queued outside the Llantrisant hospital on Monday.
Less than two weeks ago the Welsh Ambulance Service declared a state of "special emergency" after record demand in Cardiff and the Vale.
People were urged to dial 999 only in life-threatening cases after calls reached "unprecedented levels".
The Welsh Assembly Government said it was monitoring the situation.
On Monday, patients taken to the Royal Glamorgan Hospital confirmed that it was "struggling" to find beds and had attempted to divert patients to other hospitals.
Adrian Jones, director of support services, said: "It is simply the level of demand. We have had something like 195 emergency admissions in the past three days and we are struggling to find beds for them all."
The hospital had tried to contact nearby A&E units to try to divert patients but they were also under pressure.
A Welsh Ambulance NHS Trust spokesman said having a number of vehicles stuck in a queue had "made things difficult" for them and they were tacking the situation as a matter of urgency.
He said: "We have sent a locality ambulance officer there to try to minimise the problem and to liaise with the hospital bed manager.
"Sometimes it is possible, if there are a number of ambulances queuing, to leave a crew to look after more than one patient so the others can get back on the road and this has been done."
At the University Hospital of Wales in Cardiff, the situation was said to be busy but there was no unexpected pressure on A&E.
And in Newport at the Royal Gwent Hospital, staff were said to be busy but coping.
Dave Galligan, of health union Unison, said if the Royal Glamorgan was full it should be declared closed to new admissions.
He said: "People who are being delivered by ambulance could be diverted elsewhere. There are three large hospitals all within 12 miles of the Royal Glamorgan."
Plaid Cymru AM Helen Mary Jones said hospital beds were 100% full all of the time so in the event of a rise in demand, there was no give in the system.
"There are other factors here - for instance the GP out-of-hours service is so poor now. A lot of those people could probably have been dealt with in the community in previous years and can't be dealt with now.
"But this situation is not a one off. We saw the same situation two weeks ago in Cardiff and the Vale. This is something the assembly government have got to get a grip on."
Conservative health spokesman Jonathan Morgan said the problem was that many hospital beds were being occupied by people who had been treated but needed to be elsewhere for rehabilitation.
"Those people who are what we call delayed discharges and are not able to leave hospital for a variety of reasons, and hospitals, especially in the south of Wales, are struggling to get those patients moved on."
Liberal Democrat health spokeswoman Jenny Randerson said: 'The minister told us recently that ambulance and A&E delays were a freak occurrence due to bad weather and wouldn't happen again. The past few weeks have proved him wrong.
A Welsh Assembly Government spokesman said it would continue to closely monitor the position on a daily basis and received reports from the co-ordination team.
Pontypridd and Rhondda NHS Trust said on Tuesday afternoon that, while very busy, the hospital was back to normal operating levels.