Peter Costello denies allegedly 'assaulting' journalist at Canberra Airport

In the footage, journalist Liam Mendes from The Australian appears to be following the media boss who had just landed in the capital on Thursday evening.

Mr Mendes is heard repeatedly asking Mr Costello about a harassment scandal plaguing his company.

Initially ignoring the journalist from the escalator to the arrivals lounge, Mr Costello, who was Australia's treasurer from 1996 to 2007 in the Howard government, can eventually be seen approaching Mr Mendes in the frame.

The next thing we see are the journalist's feet in the air.

"You've just assaulted me," Mr Mendes said to Mr Costello in the footage captured by the journalist.

In another video, witnesses at the airport are heard telling the journalist they saw the Nine chairman "shove" him to the ground.

"F---ing oath, we saw it," one man said.

Mr Costello left the airport and arrived at the press gallery at Parliament House for the opening of the refurbished Sydney Morning Herald and The Age offices.

Upon arrival, he was immediately surrounded by journalists who asked if he had assaulted a journalist at Canberra Airport.

"Just get in front and I'll talk to you all," he told a hoard of media cameras.

He said when he landed at the airport there was "a reporter walking backwards with his phone filming".

Mr Costello said as he walked past Mr Mendes, the journalist walked back into an advertising [sign] and he fell over.

"I did not strike him," he told members of the media. "If he's upset about that, I'm sorry."

Mr Costello then walked away quickly to attend his engagement.

Some journalists have taken to social media to comment on the incident in Canberra.

The face of ABC's Media Watch Paul Barry said it was "not ideal for the chair of a media group".

Channel Ten's national affairs editor Hugh Riminton said the incident was a "terrible look" for an ASX-listed chairman "when he's managing a scandal over executive misbehaviour".

At the airport, the reporter accusing Mr Costello questioned him about a senior executive at Nine, Darren Wick, who is facing sexual harassment allegations from current and former staff at the company.

Mr Wick resigned as Nine's head of news and current affairs in March this year.

The ABC reported in late May that Nine had written to all staff acknowledging some may have experienced "trauma" in the past.

"We recognise we need to do more," read the memo, which the ABC reported was signed by Mr Peter Costello and Nine chief executive Mike Sneesby.

At Canberra Airport, Mr Mendes asked Mr Costello: "Were you aware of the allegations against Mr Wick before he left Nine? Do you support Mr Sneesby as CEO of his handling of the Darren Wick Saga? Why won't you support Mr Sneesby publicly?"

Mr Sneesby has previously said he had been unaware of the allegations against Mr Wick before media reported them.

In 2016, reporter Liam Mendes was part of court proceedings involving celebrity fitness instructor Michelle Bridges.

SBS reported she felt "threatened" and "violated" at times when the "paparazzo" photographed her in public. A local court dismissed her application for an apprehended violence order against Mr Mendes.