Masked thieves stole a safe containing high-value jewellery and cash at the Petworth Park Fine Arts and Antiques Fair yesterday morning (Sunday, May 12).
According to Sussex Police, intruders used a sports utility vehicle and a pick-up truck towing a trailer to smash through gates at the A283 London Road entrance to the National Trust property 'before driving cross-country to the marquee'.
A police spokesman added: "At around 3.30am on Sunday, thieves targeted a marquee at an antiques and fine arts fair being held in Petworth Park from which they stole a safe containing high-value jewellery and cash.
"Masked suspects manhandled the safe onto the trailer before both vehicles returned to the A283 and made off in a southerly direction towards Petworth itself. It is believed the SUV involved sustained extensive front and rear end damage during the raid."
The fair, featuring more than 50 exhibitors from around the country, was being held at 700-acre Petworth Park for the fifth successive year.
Detective Sergeant Ali Hutchings, from Chichester investigations, said: "We would like to hear from anyone who saw any suspicious activity or a group of people in or around Petworth Park during the early hours of Sunday morning, the final day of the three-day event.
"We would also like to hear from anyone who is offered jewellery in suspicious circumstances, or who may have relevant closed circuit television or dash-cam footage from the Petworth area."
If you have any information, you are asked to contact Sussex Police online or by phoning 101, quoting Operation Snowman.
Alternatively, you can contact the independent charity Crimestoppers anonymously online or by phoning 0800 555 111.