A sudden storm has dumped 30mm of rain on Rosehill Racecourse in 20 minutes, forcing the last two races to be called off.

Thunder and lightning preceded the rain which came just after the running of the Group Two Expressway Stakes, the feature race on Saturday.

"There are sections of the track near the home turn and the winning post which are unsafe," chief steward Ray Murrihy said.

Our Boy Malachi won the Expressway (1200m) at his first start since May last year when he suffered a bleeding attack in the Doomben 10,000.

After an enforced three-month ban, he then underwent surgery for colic.

Earlier Tessera and Honesty Prevails won the Canonbury and Widden Stakes respectively, vital races in the lead-up to the Golden Slipper.