Students from a central school at Kochi's Willingdon Island were evacuated on Saturday after they complained of suffocation due to an alleged ammonia gas leak.
The police said gas allegedly leaked from a tanker lorry.
No casualty has been reported in the incident.
Police said it was not a major leak, and the situation was soon brought under control.
Students were admitted to a nearby hospital after they complained about breathing problems, nausea and irritation in the eyes, the police added.
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