The reasons for the deaths are unknown, however there was speculation the horses died from some form of electric shock emanating from underneath the paddock.

Some horses had already made it down to the start and there were reports that others had “wobbled” on entering the paddock.

Despite running the first race, a decision was taking to call the rest of the meeting off.

A statement released at 2.10pm read: “The Newbury executive have decided that racing today has been abandoned.”

Newbury chairman Christopher Spence said: ``It's a nightmare for everybody. We can't be certain what it is, we all think it's electric, but we don't know.

“It’s easy to say carry on and hope for the best, but just hoping is not something we should or could do.

“We’ve got to look after our customers and we’ve got to look after the horses, so very regrettably we’ve called the meeting off.

“It’s defeated everyone and we don’t know the answer. We’ll have a meeting to decide if we can re-run any of the races and we’ll make further announcements as soon as we possibly can.

“We’ve looked at the cables and we couldn’t see any damage and no work has been carried out on the paddock since the last meeting.”

Nicky Henderson acted quickly to withdraw his runner in the first, Kid Cassidy, while Andy Turnell, trainer of Marching Song, said: “It looks like they’ve been electrocuted. My fellow seemed perfectly all right and I was about to leg him up but he just went straight down.”

Jonjo O’Neill, trainer of Fenix Two, said: “Kid Cassidy was in front and he took a turn.

“We thought he was bucking and kicking and he went down on his knees then he seemed to be OK.

“Mine reared up and we couldn’t get him back, it was like he was stuck to the ground. It was the weirdest thing I’ve ever seen in my life.”

Marching Song’s part-owner Graham Thorner said: “I was very fond of him and he had great potential.

“To a layman with no evidence, you would say it was electrical. The lad who was with him was saying ’I’m getting an electric shock off this horse’.

“As as a layman you would say that is what happened. The horses were kicking out at something and it seemed to be in an area leaving the paddock.

“It can’t be coincidence four horses have done the same thing and two have died, all in the same area. Three people said they were getting a shock off the horse. I hope we find out what it was but it doesn’t bring the horses back.”

Henderson said: “About a minute before it happened, Kid Cassidy was walking in the same corner of the paddock. I had my back turned but my daughter said ’your horse has gone down’.

“He got back up again and he went to the start. All the horses at the start had their hearts checked and he was fine, but he was desperately keen so I decided to take him out.

“Electrocution is the most obvious possibility. Nobody is to blame really, but I think you’d only really find out when they’ve done a post-mortem.

“The worse thing is what happened to the horses and it’s all very odd.”

Denman’s owner Paul Barber was in the paddock and said: “The girl of Turnell’s said she felt a tingling as she led them round and then Nicky’s horse went down.

“They were getting the shocks off the grass, not off the tarmac. I’ve never seen anything quite like that ever.”

Asked about rumours that a lead rein on one of the dead horses looked burned as if it had been electrocuted, stipendiary steward Paul Barton said: ``One of the reasons we couldn't continue was because of all the speculation,

“The lead rein could have snapped if it was stood on by another horse when it was on the ground.

“The rein will go away for forensic examination to establish what happened to it.

“We certainly won’t get the results of the post mortems today and after our meeting at 3pm I doubt we will be making any more statements.”

Racegoers will be given a 100% refund.

Trainer Philip Hobbs is keen that the meeting be rescheduled in the coming days.

He said: “The only thing I know is that now it has been abandoned hopefully we can get the meeting on again next week, it’s absolutely vital for all of us as we have nowhere to go and Cheltenham coming up.

“I was with Paul Nicholls, Alan King and Nigel Twiston-Davies and we were shocked when we found out it was off, but we don’t know all the facts.

“I would have been happy to carry on, we badly need to as their aren’t opportunities for there horses anywhere else.

“I spoke to Stuart Middleton at the British Horseracing Authority (race planning) – it looks possible it might go ahead again in the next few days, but I suppose for it to go ahead they have to sort out the problem here whatever that may be.”