Police said they are investigating the break-in at Royal's fish and chip shop on Royal Parade, Central Avenue which is believed to have been broken into between 3.10am and 3.40am.
A glass panel in the front door had been smashed to gain entry, but it is not yet known if anything has been stolen, police have said.
It is not known at this stage if anything has been stolen and police have cordoned off the area for forensic examination.
A spokesman for Sussex Police said: "Anyone who may have seen or heard anything suspicious is asked to contact Sussex Police online (https://www.sussex.police.uk/contact/af/contact-us/) or by phoning 101, quoting serial 93 of 02/01."
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