Two cars were set alight in two different streets in Brightlingsea.
Police were called to reports that a Volkswagen Golf, parked in Queen Street, and a Toyota Aygo parked in Spring Road were on fire just before 12.15am on Saturday.
A Ford Fiesta parked near the Toyota also suffered fire damage.
During their enquiries, police officers were told another car parked in Spring Road had been entered and searched.
Nothing is believed to have been stolen.
Officers are now asking residents to be vigilant and double check their vehicles are locked.
They should also make sure any items of value are removed or out of sight.
Police are continuing to investigate and are keen to speak with anyone who was in the area between 11.30pm on Friday and 12.30am on Saturday and who saw any suspicious activity, or has any CCTV footage covering the area.
Contact police on 101, quoting crime reference number 42/200800/21.
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