NJC chief executive Matt Benson said the "freak accident" at the Newcastle Racecourse stables was believed to have been caused by rodents which had chewed through an electrical cable, causing a livewire to touch the back of the metal frame of stables.

Mr Benson said it was believed the horses died when they touched the stalls after they were put back in following morning trackwork.

Mr Benson rejected reports that other horses were injured and staff were advised to go to hospital.

He said people at the scene were understandably distressed but none were injured.

He had been in contract with the Perry team.

"They were obviously devastated and the whole thing was a horrible accident you just don't expect to happen," he said.

He said SafeWork NSW had been on site to investigate the accident.