Today host Karl Stefanovic has apologised unreservedly for using the slur "tranny" while on-air on Thursday, calling himself "an ignorant tool".

Stefanovic was slammed by the LGBTQI community for using the term - considered a derogatory way to describe transgender women - while joking with colleagues.

"I was an ignorant tool. And when I say 'ignorant', I really mean it. Yesterday I got it very wrong," he said on Friday morning.

The slur occurred on Thursday when Stefanovic and co-host Sylvia Jeffreys were interviewing Today reporter Christine Ahern, who was robbed by two transgender women while covering the Rio Olympics in Brazil.