The man was working inside the trench in the village of Letterston when the sides caved in. A specialist rescue crew is at the scene, along with firemen and paramedics.
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There was disappointment for Swansea City after they lost to Manchester City for the second time in a week.
Windy with outbreaks of heavy rain pushing across the area through the evening and first part of the night.
Today will be bright, breezy and dry for most and rather windy in the northwest.