One person is in intensive care in hospital with suspected carbon monoxide poisoning following an incident at Electric Picnic in Stradbally, Co. Laois.
Emergency services responded to a 999 call just before 7am this morning.
It is understood a generator on a converted double-decker bus was leaking.
Twelve people were sleeping on the bus, which had been hired from a private operator.
Two other people were taken to Portlaoise General Hospital.
One is said to be in a stable condition while the other was brought to the hospital as a precaution.