Fraudsters are pretending to raise money for flood victims after Storm Dennis.
South Wales police said generous residents have been asked to donate cautiously as much of the area continues to recover from the storm.
Agents from Merthyr Tydfil and Rhondda Cynon Taf said that unsolicited callers and visitors, claiming to collect for the flood relief fund, could be active in the area.
A recent report follows that mobile phone users who claimed to be from public service providers had operated in the area.
A South Wales police spokesman said: “Investigations are underway by the police and partners, but the public is reminded to be vigilant and to deliver information or money only to someone they are sure of who they claim to be. “.
Rhondda Cynon Taf’s (RCT) board said it had been alerted to news of unwanted calls and “online activities” asking for donations for floods.
To avoid falling victim to the scammers, the police said they always check the identification and anyone who has been authorized by the council to collect money on behalf of the flood relief will be granted a permit.
Legitimate collectors will be able to produce a certificate or permit number and all collection buckets will be sealed.
A fundraiser created by Welsh actor Michael Sheen has already raised over £ 18,000 and a number of prominent Welsh musicians will perform fundraising concerts for people affected by the floods.
A spokesman for the RCT council said: “The council has been advised of reports of unsolicited calls and online activities asking for flood donations.
“Our advice to residents is to always ask for identification and to confirm the legitimacy of anyone who collects or asks for donations.
“Residents are advised not to make payments to callers or to provide bank details on the phone under any circumstances.”