At least 33 students of Mamud Nagar High School in Nagarpur upazila of Tangail fell ill after drinking water from a school tubewell on Tuesday morning.
Two of them were admitted to Tangail Sadar Hospital in critical condition.
According to school sources, students drank water from the tubewell on the school premises before classes began. Shortly after entering classrooms, several students complained of stomach pain, nausea and vomiting. One after another, more students became sick, prompting panic at the school.
Later, school authorities discovered a foul-smelling substance suspected to be pesticide wrapped in polythene near the tubewell. A white powder-like material was also found in the water, raising concerns of deliberate contamination.
Acting headmaster Mostafizur Rahman said the sick students were immediately taken to Nagarpur Sadar Hospital and the matter was reported to education authorities.
Upazila Education Officer Nadir Ahmed said he visited the hospital after being informed and confirmed that samples of the suspected substance would be sent for laboratory testing through the UNO and health authorities.
Upazila Health and Family Planning Officer Dr. Abdul Qadir said two critically ill students were referred to Tangail Sadar Hospital, while others are under observation and receiving treatment.
Upazila Executive Officer Erfan Uddin said that necessary action would be taken after discussions with school authorities, health officials and police.
Nagarpur Police Station OC Zahurul Islam said police have inspected the scene and legal proceedings are underway.