Emergency services are taking part in an exercise based at South Hook LNG today (Thursday).
Mid and West Wales Fire and Rescue Service (MWWFRS) is among those taking part in the exercise.
The force tweeted to say the exercise was to test the facility's COMAH (Control of Major Accident Hazard) plan.
The force said there would be increased traffic to the site until about 1pm but no cause for concern.
Pembrokeshire Command of MWWFRS said the exercise was "standard good practice which we do with all our major sites in Pembrokeshire."
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