Officers using specialist equipment are examining land around the Cariad Farm site in Marshfield, Newport.
The search - prompted by suspicion a body has been buried there - is expected to last for several days.
More top news
The Glanrhyd Bridge in Carmarthenshire collapsed on 19 October 1987 when a train plunged into the River Towy. Four people were killed.
James Rawnsey from Caldicot suffers from Erythropoietic Protoporphyria and wants a treatment developed in Australia to be offered in Wales.
Well there are no surprises as far as the weather goes! Wet and windy over the next few days. All very autumnal!