Fraudsters are pretending to collect money for flood victims following Storm Dennis.
South Wales Police said generous residents are being urged to donate with caution, as large parts of the area continue to recover from the storm.
Officers in Merthyr Tydfil and Rhondda Cynon Taf said unsolicited callers and visitors, claiming to be collecting for the flood relief fund, may be operating in the area.
It follows a recent report that cold-callers claiming to be from utility suppliers had been operating in the area.
A spokesman for South Wales Police said: "Enquiries are ongoing by police and partners, but the public are reminded to be vigilant and to only hand over information or money to someone they are certain is who they claim to be."
Rhondda Cynon Taf (RCT) council said they had been alerted to reports of unsolicited calls and "online activity" asking for flood donations.
To avoid falling victim to the scammers, police said to always check identification and anyone authorised by the council to collect money on behalf of the flood relief will have been granted a permit.
Legitimate collectors will be able to produce a certificate or permit number, and all collection buckets will be sealed.
A fundraiser set-up by Welsh actor Michael Sheen has already raised more than £18,000 and a number of Wales’ leading musicians are to appear at fundraising concerts for those affected by the floods.
A spokesman for RCT council said: "The council has been alerted to reports relating to unsolicited calls and online activity asking for flood relief donations.
“Our advice to residents is to always ask for identification, and to confirm the legitimacy of anyone collecting or asking for donations.
“Residents are advised not to make payments to cold callers or give their bank details over the phone under any circumstances.”
