Saturday's racing at Newbury has been cancelled following a dramatic incident in which two horses collapsed and died in the paddock before the first race.

Both Fenix Two and Marching Song mysteriously fell to the ground and died, with speculation that they may have been electrocuted. Some horses had already got to the start but there were reports that other runners had "wobbled" on entering the paddock. The first race was run with Al Ferof running home the winner, but the stewards then met to review the situation.

The stipendiary steward Paul Barton said prior to the meeting being halted: "The veterinary team are in charge of whatever precautions as far as the other horses are concerned. They have checked all other horses in this race." Nicky Henderson, however, withdrew his runner Kid Cassidy, who appeared to be affected by the same problem.

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."

There is speculation that the two horses may have died from some form of electric shock from a cable running underneath the parade ring.

Denman's owner Paul Barber was in the paddock and said: "The girl of [Andy] 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."

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."