The theft occurred some time during Thursday night, and police began investigations on Friday morning.

A crowbar was found behind the concrete base, while a large chain was seen in the car park the morning after the monument was stolen.

Marks in the car park and on Lawrence Hargrave Drive indicated the monument, which was first erected on August 3, 1940, had been dragged for several hundred metres.

Recently, Wollongong councillor Leigh Colacino has championed a push to have Sydney's second airport named in honour of Lawrence Hargrave, who achieved flight with one of his box kites at Stanwell Park in 1894.

Cr Colacino said the theft had left him with a deep sense of anger.

"This just stinks," he said.

"I'm dumbfounded by it - why would you steal something like that for trash value ... unless they're the biggest Hargrave groupie in the world.

"You've just got to hope the metal merchants are aware of it and are on the lookout for it, then report it back to council."

The Bald Hill tourist area was awarded $2.2 million as part of the $100 million Illawarra Infrastructure Fund, and Cr Colacino said he hoped that the monument could be replaced using some of that money.

It's not the first time thieves have targeted the monument, with the plaque beneath the statue stolen several years ago.

Sydney hang-glider operator Chris Boyce said the theft was an insult to tourists who visited the site.

"It's disgusting," Mr Boyce said. "You can't help but take it personally when people do this.

"It's terrible; it's just an insult to people who come and visit the place."

Steve Davis, a Sutherland resident who stopped at Bald Hill while cycling on Friday, was also shocked to find the monument missing.

"It's a national monument, why anyone would want to steal a national monument is beyond me," he said.

Wollongong police inspector Dan Richardson said the crowbar had been seized and would be forensically examined.

He encouraged anyone with information to contact Wollongong police or Crimestoppers on 1800 333 000.