Fire department commander Cleyton Bezerra said nine people were missing, though it was unclear if they were under the rubble or just unreachable by relatives and friends. Eight survivors have been found along with the unidentified body.
"It is a difficult situation; there are parts (of the building) that can still collapse," said Bezerra, who led the rescue operation.
Authorities in the city of 2.6 million inhabitants in Brazil's northeast said two trapped people were communicating with relatives and rescuers by phone.
"For now we are trying to hear sounds that indicate where people are. There are several layers of debris," said fire department spokesman Romario Fernandes. He said the rescue operation is expected to last days.
Witnesses said they saw people in the building shortly before it collapsed.
Neighbor Daiane Moreira was working next to the building when the building came down.
"I just heard a boom and the building came down at once. A man came out drenched in blood and with a broken arm; he was the only one we could help," Moreira told journalists at the scene, as relatives and friends of building residents wept and waited for information.
It was not immediately clear what caused the building to collapse.
The building is located in central Fortaleza about 2 miles (3 kilometers) south of the Iracema beach, one of the city's top tourist spots.