Former Formula One world champions Lewis Hamilton and Jenson Button have backed a fund to raise money for a teenage British Formula 4 driver who has had amputations to both of his legs.

Billy Monger, 17, was involved in a high-speed crash at Donington Park on Sunday.

Monger's JHR Developments team set up a JustGiving page on Wednesday afternoon with the aim of raising £260,000 and the target was reached within hours.

At time of writing well-wishers have donated more than £645,000.

Mercedes driver Hamilton, who has 4.32 million followers on Twitter, tweeted about Monger after hearing of the driver's injuries.

Hamilton tweeted: "I have only just seen the news of this tragic incident."

He later added: "Thoughts and prayers are with you and your family, @BillyMonger".