At 8.25pm today, police responded to reports of a fire at a flat above a shop on New Road, Ynysybwl, Pontypridd.
A man and a woman were rescued from the premises by the fire service.
The man remains in a critical condition at Royal Glamorgan Hospital
The woman, a 28 year old local woman from the Swansea area, who was also taken to hospital following the incident, has been discharged from hospital and been arrested on suspicion of Arson with Intent to Endanger Life.
She is being held at Cardiff Bay Police Station.
An investigation is currently underway to establish the circumstances surrounding the incident.
Detective Inspector Mark Lewis of South Wales Police Specialist Crime Investigations Team said:
“This is clearly a shocking incident but I would reassure the community of Ynys-Y-Bwl that a thorough investigation has been commenced and an increased police presence will remain in the area over the coming days. I would appeal to anyone with information to contact South Wales Police on 101 or Crimestoppers anonymously on 0800 55511.”
An Incident Room set up at Cardiff Central Police Station.
