"It's perhaps the biggest city fire in the history of Manaus," said the deputy chief of the local emergency service, Hermogenes Rabelo.

The inferno started late Monday and was only brought under control shortly after midnight after a three-hour struggle by more than 100 firefighters, the security secretariat for Amazonas state said.

Four people were taken to hospital for smoke inhalation.

The fire happened in Educandos, an impoverished and densely populated district near the center of Manaus that sits on the Rio Negro, a river that joins up with the Amazon River to flow out to the Atlantic Ocean.

Hundreds of people ran out of their homes in panic, grabbing what they could, an AFP photographer at the scene saw.

Access for fire services was hampered by the narrow alleyways in the district, and tow-trucks had to be used to haul vehicles out of the way.

An initial investigation suggests a pressure cooker on a stove started the fire, which rapidly spread, fanned by strong gusts of wind at the time, authorities said.