The artwork was located on a sea wall in the Suffolk town and depicted a rodent sipping from a cocktail in a deckchair but has recently been covered in white paint.
The vandal was interrupted by security guards at the scene but managed to escape, leaving detectives searching for the suspect and asking to speak to anyone in the area at the time.
In a statement Suffolk Police revealed: “Police are appealing for witnesses to an incident of criminal damage in Lowestoft.
“It took place at some point between 5:35pm on Saturday 14 and Sunday 15 August at just after midnight where a street mural painted by ‘Banksy’ was painted over with white paint.
“Police are keen to speak to anyone who visited the artwork after 5.30pm on the Saturday to help police with their investigation and to see if they could assist officers in their efforts to establish a more accurate time of when the offence took place.”
The artwork first attracted interest when Banksy confirmed on Friday that the mural - as well as ten other artworks along the coast of East Anglia - was his doing.
Crowds have since flocked to see the murals after the anonymous street artist revealed they were his doing.
A number of other Banksy artworks which have appeared in East Anglia in recent days as part of a series which his Instagram page calls “A Great British Spraycation”.
These include a model of a miniature stable, with Banksy’s name spray-painted over it in Great Yarmouth, Norfolk. A gang of hermit crabs in Cromer and in Lowestoft a child with a crowbar in front of a pile of sand, and a giant seagull.
Banksy’s work is extremely valuable and sometimes sells for thousands of pounds. In 2008 a piece of his work entitled Keep It Spotless sold at auction for just over £1 million.
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