RIO DE JANEIRO (AP) — A fire raced through a hospital in Rio de Janeiro, forcing staff to wheel patients into the streets on beds or in wheelchairs and killing at least 11 people, many of them elderly.

Four firefighters were hospitalized after battling the overnight blaze at Badim Hospital and about 90 patients were transferred to other hospitals, the fire department said Friday. Authorities are investigating the cause of the blaze.

Medical workers in surgical masks rolled equipment in the road as smoke billowed from the building after fire broke out Thursday night. Television images showed staff tending to patients sitting in wheelchairs with IV poles beside them in the street, some on sheets and mattresses. Elderly and intensive care patients were among those rescued.

In the chaos, distraught relatives tried to track down patients, unsure of whether they had perished in the fire or had been transferred to another medical facility.

A rope made from bedsheets and used in an attempt to escape the fire was still hanging from an upper floor window of the hospital on Friday morning.

The state Institute of Forensic Medicine released a list of names of 10 of the dead, some of them in their 80s and 90s.

Marcelo Crivella, the mayor of Rio de Janeiro, said a total of 11 people died. He visited the hospital on Friday morning and declared an official mourning period of three days.

A social worker and other Badim Hospital staff are assisting relatives of patients, the hospital said Friday.

The hospital is in a middle-income neighborhood and a short walk from Maracana stadium, which was used for World Cup soccer matches, the 2016 Rio Olympics and also Copa America soccer fixtures this year.

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Associated Press journalist Diane Jeantet contributed.