A group of emergency services, consumer watchdogs and safety groups want the government to make online sellers more liable for selling dangerous items.
Online marketplaces are a "hotbed" for risky electronics, such as hairdryers and straighteners with electric shock risks, and dangerous toys, it says.
The group wants sites like Amazon, eBay, Wish and AliExpress to be held responsible for unsafe listings.
Each of these retailers removed dangerous listings when contacted.
At the moment, "gaps in the law" mean that such marketplaces are not held to the same standards as High Street shops, the group said.
That means "they have no responsibility for the safety of products sold to millions of consumers via their platforms".
That is because many purchases are made with "third-party" sellers - so the website itself is facilitating the purchase, but not selling it themselves.
In a letter to government ministers, the group said the status quo "continues to place consumers at risk".
Sue Davies from consumer group Which? - one of the signatories - said legislation "is not fit for purpose and does not account for the massive shift to online shopping".
The letter is signed by the National Fire Chiefs Council, London Fire Brigade, Electrical Safety First, the British Toy and Hobby Association, and the Child Accident Prevention Trust, among others.
Issues the group says it has identified include children's toys still going on sale that had already been found to fall short of safety standards - for example, when tiny button or "coin" batteries could be accessed by a small child and potentially swallowed.
Dangerous products remain for sale on Wish
Regulators allowed to take down eBay listings
Festive lights sold online 'can be a fire risk'
It also said there are plugs for high-powered devices that have no fuses, or do not meet UK electrical standards for safety.
It says such examples are just part of a "range of unsafe products being sold to consumers every day".
The letter lays out evidence to prove its point, including:
63% of electrical products from online marketplaces were "non-compliant" and nearly a quarter were unsafe, according to Office for Product Safety and Standards research
unsafe children's toys that had been recalled from retailers were, in 69% of cases, still being sold online
Which? research discovered children's toys with toxic chemicals, dangerous "sleeping bags" for newborn babies, and smoke alarms that did not work - all for sale
British Toy and Hobby Association research on toys sold by third-party online sellers found that 88% of samples bought in a year were illegal to sell in the UK, and 48% were unsafe
"This cannot be allowed to continue," the letter said.
It said that given the shift towards digital purchases and Brexit, updates to the law are needed.
"It is time to close this dangerous gap in the law that allows online marketplaces to hold little to no responsibility for the safety of the products from which they profit," said Lesley Rudd, chief executive of Electrical Safety First.
"For too long consumers have been left to navigate online marketplaces with inadequate legal protection or confidence that what they are buying is safe."
The campaign comes days after French politicians asked online platforms to remove listings from Wish over safety concerns.
'Committed' and 'strict'
The companies accused of falling short were also given the chance to respond to allegations from the group.
Wish said it was "committed to creating a safe and fun environment for users to shop online, and continue to deploy further measures to help prevent, detect, and remove unsafe items from the platform".
EBay, meanwhile, said its security team "has performed sweeps to identify and remove other listings offering such products, informed the relevant buyers and that appropriate action has been taken against the sellers".
It says that its automatic filters have blocked millions of unsafe listings from ever going live.
Amazon said safety was important, adding: "We have proactive measures in place to prevent suspicious or non-compliant products from being listed and we monitor the products sold in our stores for product safety concerns.
"When appropriate, we remove a product from the store, reach out to sellers, manufacturers, and government agencies for additional information, or take other actions."
And Chinese site AliExpress said "We take very seriously the safety of all our customers and we work hard to ensure a safe shopping environment."
It highlighted that it was a "third-party online marketplace" rather than selling items itself, but said "we have strict platform rules that require all third-party sellers to comply with all applicable local laws and regulations".