Four cases of equine influenza have been identified in vaccinated thoroughbreds at the Newmarket yard of trainer Simon Crisford.

The findings are a blow to racing's hopes to resume on Wednesday following an enforced six-day shutdown following the three cases - which subsequently rose to six - of the infectious disease found at Donald McCain's stable in Cheshire.

The British Horseracing Authority said on Sunday night (Monday AEDT) Crisford had been named "in order to ensure the Newmarket community is aware of the yard at which an infection has been identified".

"No non-urgent journeys should be made to this yard - including by the media - and anyone who wishes to travel to the yard is advised to first contact the trainer's office," the BHA said.

"This yard is one of the 174 which has been required to undergo testing due to the fact that runners from the stable competed at the fixture at Newcastle on February 5, which had been identified as a potential risk fixture.

"At the moment the affected horses are all contained within this yard."

The news comes after what had appeared to be a positive weekend in the fight against the disease, with no fresh cases being reported either on Saturday or up to a previous BHA statement issued shortly after 4.30pm on Sunday.

Some 720 tests had returned negative on Saturday and around the same total was estimated in addition to that on Sunday, from over 2000 received by the Animal Health Trust in Newmarket.