Broadcaster Alan Jones has been accused of launching an "extraordinary attack" on a successful Queensland family in what their lawyer described as a defamation case like no other.

The Wagner family is suing Jones and Harbour Radio over 32 broadcasts aired between October 2014 and August 2015.

In his opening address to the Supreme Court in Brisbane, the Wagners' lawyer Tom Blackburn said Jones defamed the family by saying the brothers were responsible for 12 deaths in the 2011 Grantham floods when a quarry wall collapsed.

"The Wagners were the subject of an extraordinary, serious attack by perhaps the best known and most influential radio broadcaster in the country, Alan Jones," Mr Blackburn said.

Giving evidence, John Wagner broke down as he told the court Jones started abusing the Wagner family long before 2014.

He said Jones called him a "criminal, a thief, a corrupt businessman" among other things.

"He called me a murderer on national radio. It was a very targeted attempt to destroy our reputation," Mr Wagner said.

Mr Wagner broke down as he told the court how his children would come home from school and ask why people were saying he was a killer.

A railway crossing at Grantham is littered with debris from floodwaters on January 12, 2011. ( Dave Hunt: AAP Image )

But under cross-examination, Mr Wagner said he could not provide a date or transcript of when Mr Jones used the term "murderer".

"I can't show it to you today," Mr Wagner said.

Jones' lawyer Robert Anderson replied: "You can't show it to me tomorrow either because it doesn't exist."

Mr Wagner said he felt "helpless" during the abuse and that "it was a terrible place to be".

He wiped away tears as he spoke of the impact it had on his family and the sadness felt by his elderly parents.

"Those sorts of stress levels have an impact," he said.

The court heard the Grantham Floods Commission of Inquiry in 2015 exonerated the Wagner family over the deadly 2011 floods.

Jones also told his listeners Toowoomba's Wellcamp Airport had been approved by corruption and alleged the Wagners knew only two things: self interest and greed, the court heard.

The court heard Mr Jones also made allegations over Toowoomba's Wellcamp Airport. ( ABC News: Matt Eaton )

Mr Blackburn told the court Jones said the plaintiffs had stolen airspace from the Federal Government.

He told the court Jones also accused his clients of being "cruel, selfish and lawless people who pursue their goals through corruption, cronyism, intimidation and criminality".

"There is no truth at all in any of these allegations and they are allegations of the most serious kind," Mr Blackburn said.

Toowoomba businessman Denis Wagner at the 2015 Grantham Floods Commission of Inquiry. ( AAP: Dan Peled )

Mr Blackburn said the Wagner family started out in the quarry business in 1989 before becoming recognised as one of the most successful businesses in the state.

He told Justice Peter Flanagan this was a defamation case like no other due to the volume of allegations.

"The damages in our submission must be very large indeed because ... they constitute a defamation that is unparalleled as far as we are aware in this country," he said.

"Reckless in their baselessness and repetition, vicious in their accusations and highly irresponsible as journalists."

Outside court, Jones laughed off suggestions it would be hard for him not to comment about the case.

"I've got no comment to make — I normally do have a view but I've been told by my people to say nothing, so this day I'm doing as I'm told," he said.

The trial is being heard in front of only a judge and is expected to run for several weeks.