Excessive heat forced officials to call off a NSW provincial thoroughbred race meeting on Friday.

As the temperature reached 43.5C at Gosford racecourse at 2pm, stewards decided it was too dangerous to start the twilight meeting.

The meeting, held to attract central coast holidaymakers, was due to start at 2.53pm before a 6.50pm finish.

"In the interests of the safety and welfare of horses and participants, conditions were unsuitable for racing," a stewards' statement said.

Leading jockey Kathy O'Hara supported the move to postpone the meeting, posting a photo on her Twitter account which showed her car thermometer reaching 49C as she drove to the track.

"Right decision made at Gosford with extreme heat today. Not fair on the horses with temperatures in excess of 45 degrees," she tweeted.

In Victoria, race times for Monday's Wangaratta race meeting have been brought forward due to predicted extreme weather conditions.

The meeting, which was originally scheduled to commence at 1pm, will now be held from noon.

Intervals between races have been reduced to ensure the majority of the race card is scheduled to avoid the expected hottest time of the day.

It is the second time in the space of five days a Victorian race meeting has been brought forward due to forecast extreme heat.