Neath Port Talbot Council is alerting members of the public to a spate of manhole cover thefts in the Aberavon area of the town.
Around 23 thefts have been discovered by Council staff though there could be more with the possibility of injuries to people who do not see the missing covers.
A Council spokesman said: “The thefts appear to be centred on the Old Aberavon area of Port Talbot, particularly in and around Castle Street.
“There could be very serious injuries if people fall into spaces which previously been covered over.
“Also, of course, there will be a considerable cost to the authority in terms of replacement and work hours spent finding exactly where these thefts have taken place and carrying out re-instatement.
“This is an extremely alarming spate of thefts and those behind it have created a real public safety issue. We would like anyone who may have seen people acting suspiciously in the Old Aberavon area to contact their local police.”