A teenager killed while riding a hoverboard was reportedly out buying milk for his mum when he fell in front of a bus and was dragged 200 yards along the road.
Nawaf Al-Tuwayan, 15, fell off his self-balancing scooter and into the path of an oncoming 224 in Glacier Way, Alperton, on Thursday (December 10) evening.
Witness Jeffery Mingle said the teen "did not look confident" on the popular gadget before falling into the road.
Mr Mingle, 33, told reporters he chased the bus down the road to alert the driver, who was unaware he had struck Nawaf.
But by the time the bus was lifted and Nawaf was pulled from beneath the vehicle it was too late.
"I knocked on his door, shouting 'you need to stop, you need to stop'," Mr Mingle told The Telegraph.
"The boy was under the bus. It was terrible. It took them 15 minutes to raise up the bus, and another 20 minutes to get the boy out."
The driver of the bus has not been arrested. A colleague said he was "very experienced" and said it would be "devastating for him as well as the family of the boy".
A cousin in Saudi Arabia, where Nawaf is originally from, tweeted: "We ask God to give up patience and to help his family to give them patience and fortitude.
"We pray he enters paradise."
The teenager is believed to be the first person to die while using a hoverboard in Britain.
The vehicles have exploded in popularity in recent months and have become a novel new feature on the streets of Britain.
They are also popular with celebrities such as Lily Allen and are expected to be big sellers this Christmas.
But officials have become increasingly concerned about the craze and have questioned their safety on numerous occasions.
An increasing number of airlines have now banned them over fears their batteries might explode and cause fires.