Police experts say a blaze that killed 11 people in a Rio de Janeiro hospital was triggered by the explosion of a generator in the building's basement.

The preliminary conclusion was reached Saturday despite difficulties accessing the basement of the Badim hospital because of accumulated water and poor visibility. Police officials were still investigating why the generator failed.

The fire began Thursday night and spread through the hospital, forcing staff to wheel patients into the streets on stretchers. Many of the 11 dead were elderly.

Hospital employees work next to medical equipments at the Badim Hospital, where a fire left at least 11 people dead, in Rio de Janeiro, Brazil, Friday, Sept. 13, 2019. The fire raced through the hospital forcing staff to wheel patients into the streets on beds or in wheelchairs. (AP PhotoLeo Correa)

Hospital employees work next to medical equipments at the Badim Hospital, where a fire left at least 11 people dead, in Rio de Janeiro, Brazil, Friday, Sept. 13, 2019. The fire raced through the hospital forcing staff to wheel patients into the streets on beds or in wheelchairs. (AP PhotoLeo Correa)

Most victims died of asphyxiation as smoke filled the wards, and some died when life support equipment stopped working in the fire.

The hospital is a short walk from Maracana stadium, which was used for World Cup matches and the 2016 Rio Olympics.