At least 460 schoolgirls were affected by toxic fumes from a chemical spill near two schools in southeast Delhi's Tughlaqabad area.
The students were taken to hospitals in the neighbourhood. Barring three, who are still under observation in the Intensive Care Units of two hospitals, the rest have been discharged.
The police said a call was received at 7:35 AM about a suspected chemical leak in the customs area of the Tughlaqabad depot, which is located near the Rani Jhansi School and Government Girls Senior Secondary School, both run by the Delhi administration.
Soon, students started to complain of breathlessness and irritation in the eyes and were rushed to hospitals.
It later transpired that a chemical spill near the schools had led to toxic fumes rising in the air.
The National Disaster Response Force (NDRF) said a truck carrying 80 cans of chloromethyl pyridine had left the Tuglaqabad Depot on its way to Sonepat at 0330 hours.
"After coming out of depot the driver parked the truck on the roadside near the Railway Colony in Tuglaqabad to have tea. During this halt, some chemical spilled on the side of the road. After having tea, the driver left for Sonepat," it said.
It is suspected that the chemical, which came from China, spilled when the containers were being loaded or unloaded.
"It was in liquid form and vaporised when it came in contact with the air," an NDRF officer said.
The NDRF said a team had decontaminated the affected area, and disposed of the soil.
"Tughlaqabad area is safe now. All containers have been emptied and washed," NDRF Director General R K Pachnanda said.
Meanwhile, the affected students said they were taken to four hospitals -- the Hamdard Institute Of Medical Sciences and Research, Apollo, Batra and ESIC. One student was referred to Safdarjung Hospital.
"They complained of irritation in the eyes, breathlessness and pain in the abdomen. All of them were put on conservative treatment," said an official of the Hamdard Institute Of Medical Sciences and Research, where around 250 students, aged between 9 and 15, were admitted.
The distressed parents of the affected students blamed the school authorities for "carelessness".
"It looks like the container started leaking early morning and the people nearby put mud and water to stop the leak at that time, but they could not anticipate its impact," said Narender Singh Rawat, a computer hardware serviceman, whose two daughters were hit by the fumes.
Another parent, who did not wish to identified, questioned the failure of the schools in not anticipating such disasters.
"It is common sense that a container depot would have all kinds of consignments. Permission should not be given to schools to function in the neighbourhood," he said.
The Delhi government, which ordered a magisterial probe into the incident, has issued a show cause notice to the authorities of the Tughlaqabad depot. The Police have registered an FIR in the matter under various sections of the IPC and the Environment (Protection) Act.
The southeast district administration issued a show cause notice to the Customs Department and the Container Corporation Of India Ltd (CONCOR), the custodian of the depot.
"We will take strict action in the matter as hazardous chemicals were stored in the depot," B S Jaglan, district magistrate (southeast), said.
A CONCOR spokesperson said it was a cause of concern and they were looking into the leakage. "We will cooperate with the probe," he said.
Meanwhile, the hospitals said most students had been discharged after treatment.
"Therapeutic interventions as per clinical requirements was administered on them," Apollo said in a statement.
Union Health Minister J P Nadda had earlier instructed all Centre-run hospitals to be ready to help those affected. A team of doctors from AIIMS has been put on stand-by to cater to any emergency.
Delhi chief minister Arvind Kejriwal said strict action would be taken against those found guilty in the incident.
"We have asked the DM to take strict action against those found guilty of negligence," he told reporters after meeting the affected students in a hospital.
His deputy, Manish Sisodia, said a team from the All India Institute of Medical Sciences was carrying out a study on the medical impact of the fumes