A race meeting at The Valley in Melbourne has been abandoned because of the forecast for extreme heat while a city meeting in Adelaide has been postponed.

Friday's night meeting at The Valley was called off on Thursday, with temperatures predicted to reach 43 degrees in Melbourne on Friday and remain in the high 30s until a cool change around 10pm.

"The hottest part of the day is predicted to be late afternoon when many horses would be required to travel and the temperature is predicted to be around 40 degrees when the meeting is scheduled to start at 7pm," Racing Victoria's Greg Carpenter said.

RV said Friday's meeting at Yarra Valley was scheduled to proceed with hot weather protocols in place.

Race times for the Yarra Valley meeting were adjusted earlier this week, with the meeting to begin at 10.30am, two hours earlier than originally planned, with the final race at 2.40pm.

RV said the BOM is predicting the temperature will be 27 deg at the start of the Yarra Valley meeting and rise to 37 deg by the end.

Because of the extreme heat, South Australian racing officials have transferred Friday's scheduled seven-race twilight race meeting to Monday afternoon.

A meeting at Dubbo in NSW on Saturday has been abandoned because of a predicted 45 degrees and no suitable alternative dates available.

Saturday's Sydney metropolitan meeting has been moved from Warwick Farm in the west to Randwick which is expected to be up to 10 deg cooler.

Racing officials in NSW, Victoria and South Australia have been juggling start times of recent meetings to try to avoid the hottest parts of the day.