The fire in Nagli area near Dhansagar station in Chandpai range of the Sundarbans has been brought under control.
Chandpai range officer Gazi Motiar Rahman said the fire originated in Nagli area on Sunday evening.
Fire fighters managed to bring the fire under control on Monday morning.
However, the origin of the fire and how far the fire spread could not be ascertained yet.
Forest department officials and fire fighters are on alert, Motiar Rahman said.
Morelganj Fire Service Station Officer Swapan Kumar Bhakta said: "The fire is now under control. Smoke is hovering over some areas."
Sundarbans east range Divisional Forest Officer Md Saidul Islam said they have cut a fire lane to stop the spread of the fire.
He said a three-member committee was formed to carry out an investigation into the matter.
The committee has been asked to submit a report within three working days.