A police spokesman said incidents have occurred at sites included the West Dean Nature Reserve, Stoughton Down, Stansted Park, West Stoke, Bignor Hill and the South Harting car parks.
The spokesman added: “Officers would like to remind all vehicle owners not to leave any valuables in vehicles when visiting beauty spots in the area.
“Consider leaving handbags or purses at home or take them with you when leaving cars unattended.
“All lines of enquiry, including CCTV footage, of these incidents will be investigated.”
Stating it had seen an increase in thefts from vehicles, Chichester Police took to social media to urge motorists to ‘remain vigilant’.
Anyone who has witnessed, or been victim, of a break-in, is asked to contact police online or call 101 quoting reference Operation Mini.
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