"They've done really, really well," said spokeswoman Marianne Poole.
"We've had a real explosion Dannevirke, Bay of Plenty, and Wellington. Taranaki are bringing people down."
Two big names to watch will be Wellington's Paul Mountfort and Whakatane's Max Stott.
Mountfort is the 2012 and 2013 Mr New Zealand Athletic champion, while Stott, the 2004 Mr Universe Masters champion, is coming out of retirement for this event.
The event will cover all classes of body types, fitness, shape, figure, athletic and physique.
Today, the judging round will be from 1-3pm, with the night show starting at 6pm. Entry to the public in the afternoon is $15 and the evening show is $20.
Wanganui entrants representing gyms are:
Joel Ashworth (Junior), Mark Benson (Athletic Open Short), Vicky Boswell (Physique Women Senior 40+), Isaac Chamberlain (Teenage Men), Sasha Crafar (Physique Women Novice Short), Jan Dixon (Physique Women Open Short), Darren Faulkner (Athletic Masters 40+), Courtney Harvey (Ms Fitness), Kirsty Harvey (Ms Fitness), Mark Kaipo (Athletic Novice Tall), Michael Little (Athletic Novice Short), Audrey O'Keefe (Figure Senior 40+), Michaela Sullenberger (Teenage Women), Taonga Takiari (Physique Men Novice Tall), Thomas Tataurangi (Physique Men Open Tall), Maureen Thomas (Figure Senior 50+), Brendan Udy (Physique Men Novice Tall).