Thieves targeted two roadside cafes and stole their generators.
They struck between 2pm on Tuesday and 7am ttoday at Vinnys on the Chelmsford bound carriageway, between Kelvedon and Witham, and Dennies on the opposite carriageway between Witham and Kelvedon.
Police officers want to speak to any motorists who saw anything suspicious in the laybys.
Investigating Officer Pc Garry Shuttleworth at Braintree Police Station said: "Both generators are large and would have taken a number of people to move and therefore I am hoping that someone may have seen unusual activity in the laybys."
If you saw something that you may think will help please contact Pc Shuttleworth on 101 ext 400250.
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