Do not adjust your radios — Alan Jones really did just use the N word live on air.

The controversial 2GB Sydney breakfast host was speaking about the leadership saga in Canberra when he used an offensive phrase.

It sparked immediate outrage on social media and calls for people to boycott advertisers on the top-rating program.

"They are mobilising to block Dutton," Jones said.

"The n****r in the woodpile here, if I can use that expression, and I'm not going to yield to certain people who tell us that words in the language are forbidden, the person who's playing hard to get, is Mathias Cormann."

The phrase originated in America's deep south in the 19th Century and was used to describe slaves who had fled their captors.

Escapees were said to have hidden in piles of firewood while travelling north to Canada. In a modern context, it is almost universally considered racist and hurtful.

A British politician who used the phrase in parliament 10 years ago faced furore and was called on to resign, before issuing a grovelling apology.

Users on Twitter described Jones' remarks as "disgusting" and "disgraceful", saying he should be sacked or seriously sanctioned.

Jones has apparently used the term on previous occasions and also refused to apologise for it. He uttered it during an interview with Tony Abbott in 2012.

Macquarie Media Limited, which owns the 2GB station, has been approached for comment.

Aye so this is where we are now? People like Alan Jones are ok to say the N-word on 2GB? In 2018? Absolute disgrace. True colours.

— Brett Lovett (@brettalovett) August 23, 2018

I stepped away to get a cup of tea, and got back to find Turnbull's still in charge, but Alan Jones dropped the N word on the radio.

— Liz 🦑 (@_lizbarr) August 23, 2018

Alan Jones has used that revolting expression a few times before. I heard him use it while I was in a cab a few years ago and was shocked, especially by the fact that nothing then happened.

— Matthew Denby (@MrMattDenby) August 23, 2018

Late this morning, Jones took to Twitter to apologise for the remark.

"We all make mistakes. This morning on 2GB and 4BC I spoke about the covert actions of some political operatives in the current leadership challenges within the Liberal Party.

"I used an old and offensive figure of speech that I regret saying. People should be honest and forthright in their actions and that is not happening in the Liberal Party right now. I will have more to say on this tomorrow."

It's not the first time the firebrand shock jock has attracted controversy.

He was forced to apologise after being caught on tape at a Young Liberals fundraiser in 2012 saying then-Prime Minister Julia Gillard's father had "died of shame".

That same year, Jones also issued an apology for describing Lebanese people as "vermin" and "mongrels".

The veteran broadcaster is currently being sued by the Wagner family, a prominent agricultural dynasty in Queensland, over comments he made in dozens of broadcasts in 2014 and 2015.