"The gas is spreading from the DPA (Diammonium phosphate) factory causing breathing problems of the people within several kilometres in the neighbourhood. Fire fighters are trying to stop the emission," officer-in-charge of the nearby police station said.
The people were admitted to the state-run Chittagong hospital on the banks of Karnaphuli River last night.
The TV reports quoting the factory officials said one of the gas tanks with 500 tonne capacity leaked at around 11:30 PM while the ammonia gas spread across to the other bank of the Karnaphuli.
Experts said exposure to ammonia could cause slackening, vomiting and breathing problems.
"I have been informed that the fire service men nearly brought under control the situation," Chittagong's deputy commissioner Mesbahuddin Ahmed said.