Search teams were seen digging in a back garden as part of an investigation led by the National Crime Agency.
Officers examined a property in Warrington for much of Monday as part of a what appeared to be an extensive operation.
Fence panels were also seen being moved and carriers bags of potential evidence being taken away from the house.
The search began at around 7.30am, when witnesses said police arrived at a home on Selworthy Drive in the Thelwall area of the town.
That presence remained at the scene for most of the day, with both North Wales Police and Cheshire Police maintaining a presence there.
The investigation is being led by the NCA, which tackles top-level criminality across the UK.
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A spokeswoman for the force confirmed it was overseeing a search of the home but said further information could not be provided at this stage of the investigation.
She said: “As part of a National Crime Agency investigation a search is underway at a property in the Thelwall area of Warrington. While the operation continues we are currently unable to provide further details.”
