Hong Kong firefighters will investigate the cause of a blaze that broke out Friday at a warehouse and forced 3,400 people, including students, to evacuate, authorities said.

Hong Kong authorities evacuated at least 3,400 people from buildings after a fire broke out in a warehouse in the city's Kowloon district on Friday.

Thick smoke was seen pouring out from the building where the fire broke out around 2 p.m. at the warehouse on Fat Tseung Street in Cheung Sha Wan, a residential and industrial area in Kowloon, the government said.

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.

It took five hours for firefighters to put out the blaze. No casualties have been reported so far.

The state-owned company China Resources Group owns the warehouse, according to the Reuters news agency, but the details of how the fire started or what was stored there are unknown.

The company is involved in running businesses from health care to consumer products, such as beer.

Hong Kong has one of the world's highest population densities.

The government provided temporary shelter to affected residents at a sports complex. They also advised the people to stay indoors to protect themselves from the "smoke and unusual odor."

"There is a chance that the number of people involved in the evacuation will rise further," police said. 

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.