Initial investigations suggest spontaneous combustion may have caused the fire, police said.

A fire service investigator was also looking into the blaze, but had not yet found evidence to support the spontaneous combustion theory put forward by police.

The alarm was raised about 3.40pm with nine fire crews fighting the flaming cardboard on Luke Street in Lytton and using heavy machinery to try to separate the scrap material.

Police closed nearby Lytton Road from Gosport Street to the Port of Brisbane due to the poor visibility and put diversions in place.

The fire was extinguished and crews were dampening down hotspots about 9pm, with a fire investigator called to look into the cause of the fire.

Paramedics remained on standby as firefighters fought the flames but no one was injured.

Fire crews were also called to a vegetation fire on the same street about 10 minutes after they were called to the cardboard fire.

The vegetation fire, which originally had seven crews in attendance, was successfully extinguished about 5pm.