Thousands of hoverboards - tipped to be one of this year's most popular Christmas presents - have been seized by authorities over concerns they could explode.
National Trading Standards (NTS) said 15,000 of the 17,000 self-balancing scooters examined since October 15 have been detained, mainly for having non-compliant electrical components which could explode or catch fire.
Many of the boards were found to have non-compliant plugs without fuses, which increase the risk of the device overheating, exploding or catching fire, and cut-off switches which failed when tested.
Chargers, cabling and batteries were also found to fail safety standards.
Many of the seized items carried apparently fake CE marking, and NTS advised that "unfortunately consumers cannot rely on the CE mark as an indication that a hoverboard is safe".
NTS said there had been a "huge spike" in the number of hoverboards arriving into the UK in recent weeks, destined to end up as Christmas gifts, and additional staff were being trained to carry out testing.
Last month Kent Trading Standards warned about dangerous replicas of hoverboards - popularised by Marty McFly in the 1980s film Back To The Future starring Michael J Fox - selling for hundreds of pounds cheaper than the normal price of £300 to £600 on auction sites and social media accounts.
In Deal, Kent, one hoverboard bought online caught alight while charging, causing some £25,000 worth of damage to the owner's kitchen.
NTS chairman Lord Toby Harris said: "Our teams at sea ports, postal hubs and airports have seen a significant spike in the number of unsafe hoverboards arriving at national entry points in recent weeks and are working around the clock to prevent dangerous items from entering the supply chain.
"We suspect that most of these products are being imported for onward sale domestically as Christmas approaches. We urge consumers to be on their guard when purchasing these products and advise you read our product safety checklist to help ensure you are not purchasing a dangerous item."
Consumer Minister Nick Boles said: "Shoppers should think twice before choosing products from a site that does not appear genuine, and the checklist that National Trading Standards has produced is extremely useful.
"I urge anyone who suspects a hoverboard not to be genuine to report it to the Citizens Advice consumer helpline."
Consumers should check that the three pin plug on the device states it is made to BS 1363 and avoid buying it if this information is missing.
They should also:
* Never leave the device charging unattended, especially overnight. A faulty cut-off switch or plug without a fuse - seen in many of the seized boards - could lead to it overheating, exploding or catching fire.
* Check the shape of the plug. The first unsafe boards identified often had a clover-shaped plug.
* Check for online reviews that seem genuine and for information about the company's head office and landline number. Sites that have spelling or grammar mistakes, including in the small print, can be an indication that it is not a professional operation.
* Never be dazzled by a bargain. If the price is too good to be true, it probably is.
* Report any concerns to Citizens Advice on 03454 04 05 06.