The Hospital Authority on Tuesday said a four-year-old girl suffered a cardiac arrest after receiving stitches in Yan Chai Hospital.

The authority said the medical staff resuscitated her and that she regained a heartbeat 18 minutes later, but remains in a coma and in critical condition.

She was sent to Yan Chai Hospital’s accident and emergency department after sustaining a head injury in a fall on Saturday night. The child had a slight fever and medical staff put stitches into a two-centimetre gash in her head.

The hospital's chief executive, Ian Cheung, said this incident was "very rare", adding the staff had followed procedures when giving her three stitches.

"It was a very short process... She cried during the first stitch, but she quieted down during the second and the third stitches," he told reporters.

"We checked her after completing the process because it's over so quickly, and we found out she didn't have a pulse. So we must find experts to give us advice on why this happened."

The girl was then transferred to the paediatric intensive care unit at Princess Margaret Hospital.

Fong Nai-chung, chief of service for paediatrics in both Princess Margaret and Yan Chai hospitals, said she suffered from ischemic encephalopathy, which meant her brain was injured because blood supply decreased when her heart stopped.

"Currently, she is on a ventilator, given heart medication and drugs to control seizures and swelling in the brain. These are also coupled with antibiotics and nutrient injections. Our team will monitor her situation closely and provide the most appropriate treatment for her," he said.

The Hospital Authority said it is upset by the incident, and is providing assistance to the girl's family.