Nigel Pascoe QC, told Gloucester Crown Court: 'There was a scene of dreadful devastation.'
Shaun Gooch, 25, and Anthony Gallagher, 23, deny causing death by reckless driving.
Mr Pascoe said that on Friday 13 September last year Mr Gooch and Mr Gallagher were racing their Ford Escorts at speeds of at least 80mph on Akers Way, Moredon, which has a 40mph limit. 'The speed was such that Gooch's vehicle seems to have taken off just before the impact.'
Ian Lilley, seven, Sheree Lear, eight, and Paul Carr, 17, died instantly. Paula Barnes, 16, and Belinda Brown, 19, died in hospital. Mr Gooch required hospital treatment but was not seriously hurt after being thrown clear of his car.
Mr Pascoe said: 'The only sensible explanation is not simply that Gooch was going far too fast but that the two men were racing. Gooch has accepted his speed was over 40mph.'
Peter Simpson, a witness, told the court he saw two Escorts leaving a roundabout at about 50mph and close together. 'I heard a screech of tyres and saw two cars virtually nose to tail come off the roundabout and along Akers Way. I could see the drivers. The first was looking in the rear-view mirror, laughing and watching the car behind. The second was smiling and laughing. I got the impression they were racing.'
Witnesses saw the two cars approaching at speed. The vehicle driven by Mr Gooch changed down a gear and moved to overtake both Mr Gallagher's XR3i and another Ford Escort waiting to turn. They saw the car go out of control and strike the kerb. It then spun and appeared to become airborne before hitting the bench where the youngsters sat.
Mr Gooch, of Burbage Road, Penhill, Swindon, told police he remembered going down Akers Way and putting his foot on the brake; his foot got stuck and he looked down to investigate. He could remember nothing more.
Mr Gallagher, of Beech Avenue, Pinehurst, Swindon, told police that the two cars had touched as Mr Gooch was overtaking. 'I heard a scraping noise and saw the car at the side of me. I began to brake and then I saw it go off to the side towards the bench. I closed my eyes.'
The trial continues.