Council leaders have reported a 40% increase in reported scams since the start of the coronavirus crisis.
The Local Government Association (LGA) said ruthless criminals are exploiting the pandemic by selling unsafe and fake products to the public.
Scams include selling fake coronavirus test kits and hand sanitisers, bogus medical products claiming to treat or prevent Covid-19, and false communications about funding and grants.
The LGA said one council alone has seized more than half a million substandard face masks.
Cllr Simon Blackburn, chair of the LGA’s Safer and Stronger Communities Board, said: ‘Some councils have seen a significant surge in reports of scams by criminals exploiting coronavirus fears to prey on vulnerable and older people self-isolating.
’People need to be cautious. If something doesn’t seem right or sounds too good to be true, don’t hesitate to end a phone call, bin a letter, delete an email or shut the door.’