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.
More top news
Rain moving east, will spread across Wales in the first half of the night, some likely heavy.
Rain moving east, heavy at times
The Lesbian, Gay, Bisexual and Transgendered communities in Cardiff are celebrating 30 years of campaigning; as part of LGBT History Month.