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.
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Mainly dry with lengthy clear spells overnight and just a few showers likely, especially in the north and west.
Ysgol Uwchradd Caergybi became the UK's first comprehensive 65 years ago. Academies are now dominant in England, but certainly not in Wales.
Dry for most, but a few showers likely.