Hospital chiefs have launched an investigation after a mortuary fridge containing the bodies of five infants broke down.
The refrigeration unit at St Helier Hospital in Carshalton, Surrey, stopped working for 36 hours last Friday.
Fears have since been raised that the malfunction may affect the ability establish the causes of death.
Dr Martin Stockwell, joint medical director at the hospital, said: "With much regret, we can confirm that a technical failure in the mortuary department at St Helier Hospital resulted in one of six refrigeration units breaking down for approximately 36 hours (on) Friday 10 August.
"We are deeply sorry that this incident occurred, and we are working hard to understand how and why it happened. The Trust is taking this matter very seriously, and we are reviewing our processes as a matter of urgency.
"We have launched a thorough investigation into the matter, and are working closely with the Human Tissue Authority (the national authority responsible for regulating mortuary activities), to prevent it happening again."
The hospital is part of Epsom and St Helier NHS Trust and caters for people living in south west London and north east Surrey.
Queen Mary's Hospital for Children, which is also part of the Trust, also runs on the site.
The Trust provides neonatal intensive care to a wider area including parts of Sussex and Hampshire.