HORSHAM's Oven Door Bakery owner James Henwood has broken the world record with the world's biggest vanilla slice.

Mr Henwood started his Guinness World Record tilt at 10am Wednesday morning at the Horsham Show.

A steward has weighed and noted each mix to comply with Guinness's rules.

The final dessert was a whopping 677.76kg.

Previously, the largest custard slice weighed 508.11kg and was made by Flinders Fish and Chips, in Flinders, Victoria, June 3, 2012.

Mr Henwood said his project had created plenty of interest.

"We've had a steady stream of people come through all day," he said.

"We've already sold three quarters of the vanilla slices we brought down to sell."

Horsham Agricultural Society secretary Andrea Cross said the record attempt was a highlight of Wednesday night's festivities, along with fireworks.

She said crowd numbers were up for the second and final day of the show.

"The weather mucked us up a bit on Tuesday," she said.

She said Wednesday's show competitions were popular.

Leigh McGennisken won the Rural Ambassador Award, while Dustin Cross won the junior ambassador award.

Sarah Marchment is the young leader for 2014 and Meaghan Wik was named Miss Teen Showgirl.

Mrs Cross said the beaut ute competition was hotly contested.

Scott Morrison won the coveted Bryce Hallam Memorial award for best local ute.