Racing has been called off at Newbury in extraordinary circumstances after Fenix Two and Marching Song collapsed and died in the parade ring before the first race.

An inquiry and immediate post-mortem examinations were announced, with the reasons for the deaths unknown amid 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.

Nicky Henderson was quick to withdraw his runner 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."

He added: "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."

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."

Stipendiary steward Paul Barton said: "We are going to hold an inquiry and interview those connected with the horses. We are not going to use the parade ring for the rest of the meeting. The horses will parade in the pre-parade ring and leave from that point.

"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."