A forklift caused a partial roof collapse at a Hertz rental warehouse after smashing into a support column on October 24.

People inside the building were evacuated.

The collision broke a post that supported a roof beam, severing electrical wires and a sprinkler system pipe, said an Eastside Journal newspaper report.

Firefighters said electricity was arcing at the ceiling and a several-thousand-gallon lake was forming in the warehouse.

"We were concerned about the electrocution hazard, as well as the chance of collapse," one firefighter said.

Ten minutes after the building was evacuated, a 4,000 square foot (370 square metres) section of the roof collapsed. Kirkland building inspectors have closed the building until repairs are made and a structural engineer has declared it safe.