People and businesses should be wary of scammers trying to turn the coronavirus pandemic to their advantage, the National Crime Agency (NCA) has warned.
Scammers have been targeting vulnerable people including those self-isolating at home, the NCA said.
Graeme Biggar, director general of the agency's National Economic Crime Centre, said the virus was increasingly being used as "a hook to commit fraud".
It comes as two people were arrested on suspicion of selling illegal tests.
A 46-year-old pharmacist from Croydon, south London, was arrested on Saturday on suspicion of making false and misleading claims about the capability of coronavirus testing kits he had allegedly tried to sell, the NCA said.
Officers seized £20,000 in cash and searched two properties and a car. The suspect was released on bail.
Separately, on Sunday, investigators arrested a 39-year-old surveyor from Uxbridge, west London, who had allegedly planned to sell 250 testing kits to construction workers.
He was also held under the Fraud Act, investigators said.
No home tests have yet been certified under European safety standards - and it is illegal to sell them.
The use of home testing kits is also not advised by Public Health England.
Nikki Holland, NCA director of investigations, said: "Criminals capitalise on fear and anxiety and they will exploit any opportunity, no matter how awful, to line their pockets.
"Illegally selling testing kits completely undermines the nation's collective response to the pandemic and actually endangers lives."
Scammers are targeting people trying to buy medical supplies online and have been sending emails offering fake medical support, the NCA said.
Fraudsters have also tried to lure potential victims with pleas to support fake charities, the crime agency added.
'Offences likely to increase'
"Covid-19 is increasingly being used as a hook to commit fraud - and we think these offences are likely to increase during the pandemic," Mr Biggar said.
"Individuals and businesses need to be fully prepared for criminals trying to turn the pandemic to their advantage by scamming them out of money."
The Medicines and Healthcare Products Regulatory Agency said it was working with police to protect public health.
Tariq Sarwar, head of operations for enforcement at the MHRA, urged the public and healthcare professionals to report any online posts advertising testing products.
"Always make sure you are buying your medicines from a registered pharmacy or website and your medical devices from reputable retailers," he added.
Details of the two London arrests emerged after a separate international investigation into a multi-million-pound coronavirus mask scam.
The alleged scam began after a German company tried to buy 10m masks, valued at about €15m (£13m), from online suppliers. An Irish citizen has been questioned.