A Labor backbencher has apologised for swearing during parliamentary proceedings, after his microphone captured a curse-peppered rant about an unknown woman.

Toohey MP Peter Russo owned up to the tirade, made during the passing of the Government's controversial laws banning dangerous protest devices on Thursday afternoon.

"She's a f***wit isn't she?" he said.

"Just a f****** … (inaudible)."

"I reckon she's on something."

It also captured him making horse-like blowing noises.

Within 24 hours Mr Russo apologised on Facebook for the "unparliamentary language".

"I apologise to the Parliament for my unparliamentary language that was recorded in the House during division yesterday," he wrote.

Peter Russo has apologised and says the swearing was "unparliamentary". ( Facebook: Peter Russo MP Toohey )

"This is not the type of language a parliamentarian should be using.

"I apologise unreservedly."

It is unclear who Mr Russo was referring to.

Parliament's internal broadcast feed captured the moment his colleague Melissa McMahon waved at him from several seats away before his microphone was switched off.

Premier Annastacia Palaszczuk was in the chamber at the time but said she did not hear it and was unaware until the swearing was raised by the media on Friday morning.

"This is the first time I'm hearing about it," she said.

"I don't know, but if anyone is making unparliamentary remarks in Parliament, they're not allowed to do that and they need to apologise."

She said it was never nice to hear foul language in the chamber.

"Having been abused formally in the Parliament previously by the LNP, no it's not nice" she said.

"I think they need to find out who did it and they need to apologise if that's the case."

'Highly offensive': Opposition MP slams Russo

Manager of Opposition Business Jarrod Bleijie said the comments were the worst he has heard in the House.

"In 10 years it definitely is the strongest I have heard in Parliament since I have been there," he said.

"It is highly, highly offensive and highly inappropriate and he ought to have known better.

"Yes there is robust debate from time to time and members of Parliament will take silly objections because they have glass jaws … but these comments are beyond anything that we have heard any member of Parliament say.

"It essentially doesn't matter who he is referring to — it's inappropriate, he shouldn't have done it."