HOUSTON -

Stacks of cardboard behind a Walmart in northeast Houston caught on fire early Sunday morning.

When firefighters arrived at the store on Fulton near East Crosstimbers around 2 a.m., they said they found several bundles of compacted cardboard burning.

A forklift had to be used to separate the bundles just to put the fire out, officials said.

Fire officials said no one was hurt in the fire.

Investigators said the fire never reached the Walmart store, but smoke from the fire managed to get into the back part of the store's warehouse.

Arson investigators were called to the scene to determine the cause of the fire.