British police on Tuesday made a second arrest in their hunt for thieves who stole a functioning 18-carat gold toilet from Blenheim Palace, a UNESCO World Heritage Site.

Designed by Italian artist Maurizio Cattelan and once offered on loan to US President Donald Trump, the toilet was stolen on Saturday -- just three days after it had been put on display.

It has been valued at around $5 to $6 million and been a hit with tourists, who lined up to snap selfies of them sitting on its golden seat.

Police in Oxford, the historic city on whose outskirts the palatial palace was built in the early 1700s, announced the arrest of a 36-year-old man who was then released pending an investigation.

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"We are continuing to investigate this incident and have made a second arrest in connection with it," investigative officer Steven Jones said in a statement.

"Our priority is to locate the stolen item."

The police have also arrested and released on bail a 66-year-old man suspected of being part of the gang.

Cattelan told The New York Times that his work, called "America," was "one-percent art for the 99 percent".