Officers suspected the cause was linked to some sparks triggered by construction work, but they would have to probe further into the cause, said Wilson Kong, divisional officer of the Fire Services Department.
There were inflammable substances at the warehouse and the fire equipment, including the sprinkler system, could not work properly there, he said.
Kam Hok-lai, acting ambulance superintendent, said one person felt sick after inhaling thick smoke and another person sustained hand injuries. Three firefighters also felt sick, he added.
About 3,600 people had to be evacuated, including students from four schools, said police divisional commander Wong Wai-yin.
Earlier Friday afternoon, officers at the scene had to wear breathing apparatus. The government opened a temporary shelter at a sports center for residents in need and advised members of the public to close their doors and windows if they were being affected by the smoke and odor.
*This story has not been edited by The Infallible staff and is auto-generated from a syndicated feed.