He said those affected had only reported mild symptoms such as coughing, headaches, irritation or nausea.

“I have been informed that the situation is under control, with ammonia gas levels having returned to the baseline.

“No students have been hospitalised. Based on the reports, only minor symptoms like irritation and coughing were noted.

“Nevertheless, we will continue monitoring the situation with the department of environment and the state executive committee,” he told a press conference after a “smoke-free, clean premises” walkabout programme on Jalan Dhoby here last night.

State health and environment committee chairman Ling Tian Soon said he is awaiting the analysis results on unidentified packages found discarded along the banks of Sungai Pandan near Taman Daya yesterday.

On Tuesday, residents reported noxious fumes in areas around Taman Daya, Taman Mount Austin and Taman Istimewa here.

The Johor DOE also reported that elevated concentrations of ammonia gas were detected in Sungai Pandan at Kampung Melayu Pandan.