The Massy Stores Supermarket on New Dock Road, Vieux Fort, had to be evacuated Saturday afternoon following reports of a gas leak, emergency officials say.
A video was posted on social media.
A spokesman for the Saint Lucia Fire Service (SLFS) told St Lucia Times that Freon gas leaked from a refrigerator into the store.
The gas is said to have been most concentrated in the lunch room.
He said the fire service and health officials responded after an alarm was raised about 12:44 pm.
According to the official, one person had to be hospitalised.
He disclosed that a decision was taken to shut down all commercial activity until the situation was rectified and the supermarket properly ventilated.
Freon is tasteless and mostly odorless. When when it is deeply inhaled, it can cut off vital oxygen to the cells and lungs.