HONG KONG (AP) — Hong Kong firefighters were battling a blaze Friday at a warehouse that forced 3,400 people to evacuate, including students, police said.

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.

Two persons who worked near the site felt sick after inhaling thick smoke, and people from four schools and one residential building nearby had to be evacuated, police said.

“There is a chance that the number of people involved in the evacuation will rise further,” police said. The cause of the fire was unclear.

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 odour.