The leak occurred in a pipe connected to the lorry when ammonia was being transferred from a plant managed by Fertilisers And Chemicals Travancore (FACT), officials said.
Police said it was not a major leak. The incident occurred at around 1.30 PM.
The situation was now under control, they said.
Some people who complained of breathing problems, nausea and irritation in the eyes after the leak were treated at a health facility of the Cochin Port Trust and all of them were now fine, they said.
Steps were also taken to evacuate them through a lake, they said.
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