An electrical storm has forced the cancellation of the final race at Randwick on Anzac Day.

The storm hit Sydney late in the afternoon and moved east around 4.30pm.

Players in the Roosters/St George NRL match at the nearby Sydney Football Stadium were also called off the field to wait out the thunder, lightning and hail.

Saturday's storm comes on the back of a damaging weather week for Sydney and the NSW Hunter Valley with floods costing lives and destroying homes.

By 5pm the weather had cleared at Randwick but the horse tunnel was flooded and surface water on the track ruled out the possibility of running the eighth race after 30mm fell in 15 minutes.