At least 15 people died and 26 were injured, of whom six are in critical condition, due to a liquid ammonia leak at a Shanghai factory, local authorities said Saturday.

The leak occurred at 11:00 a.m. Saturday in a refrigeration unit of the Cold Storage Industrial Co., located in the Baoshan district of China's most populated city.

The injured have been taken to a nearby hospital for treatment, local authorities added on their Sina Weibo account, the Chinese Twitter.

What caused the leak is as yet unknown, but an investigation has been launched to find out, Shanghai city hall said in a brief communique. EFE