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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Gareth Bale insists reaching the last eight of Euro 2016 is not enough for Wales ahead of their quarter-final against Belgium.
Thousands of Queen Bey fans are expected to descend upon the capital on Thursday, as the Formation World Tour comes to Wales.
Inspectors say South Wales Police has improved how it protects children but there are still some areas that need further attention.