The blaze broke out around 22:30 local time at the El Edén home in Pitrufquen, roughly 640km south of Santiago, and was only extinguished on Saturday morning. Ten other residents were evacuated. Authorities have not yet determined the cause.
Prosecutor Jorge Granada, who is leading the investigation, said it was not clear what started the fire. Firefighters spent Saturday clearing debris, including collapsed corrugated metal roofing, and police cordoned off the area for safety.
President Kast said the government would "fully collaborate with the justice system to clarify what happened, determine where failures may have existed in oversight or prevention, identify what alerts were raised and what actions were taken in response to them."
"We need to know the truth and, based on that, correct whatever is necessary to do everything possible to prevent a tragedy like this from happening again," he added.
Local mayor Jacqueline Romero described the situation as "a situation that fills our souls with great sorrow and pain" and said authorities were supporting the affected families.
The revelation that the facility had been subject to penalties over regulatory breaches since at least 2019 adds a new dimension to the investigation, which is now examining both the fire's immediate cause and the broader oversight regime for care homes in Chile.