Investigations are continuing following a drugs raid at Plas Glynllifon near Caernarfon.
North Wales Police confirmed it had executed a warrant under the Misuse of Drugs Act on Tuesday at the 19th century mansion near Llandwrog.
In a statement on Tuesday night, the force said officers will remain at the site for several days while their enquiries continue.
A spokesperson added: "We are asking members of the public to respect the police cordon as officers carry out their work."
There are no further details at the moment.
Glynllifon, a Grade I-listed building, has remained empty since falling into receivership in 2020, when plans to turn the mansion into a hotel failed.
It was brought in 2022 by Manchester-based businessman Davis Savage, but put back up for sale just two years later.
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