The final week of election campaigning in the New South Wales mid-north coast seat of Cowper has taken a nasty turn.

Television advertisements have hit the screens and flyers have been delivered to homes across the National-Party-held electorate, making allegations against high-profile independent candidate Rob Oakeshott.

"The mud bucket has been opened," Mr Oakeshott said in a video response posted to his Facebook page.

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'He can get a bit of it back too'

The Deputy Prime Minister Michael McCormack defended the advertisement.

He accused Mr Oakeshott of launching an attack against a man he claimed to be Mr McCormack's son.

"Rob Oakeshott doesn't mind throwing it out. If he wants to give it out, then he can get a bit of it back too," Mr McCormack said.

Among the statements made in the advertising, commissioned by the National Party, are that Mr Oakeshott has "lined his pockets with [tax payers'] money, whether it be his pollie's salary, cushy pension or electoral funding".

It also accused him of never having "done a hard day's work in his life" and wanting to "top up his retirement savings out of [tax payers]".

Mr Oakeshott addressed the claims in his social media video, including the claims surrounding his "cushy pollies' pension".

"I'm actually giving up that State pension to run for Parliament," Mr Oakeshott said.

This National Party flyer has been delivered to homes across Coffs Harbour attacking independent candidate, Rob Oakeshott. ( ABC Coffs Coast: Claudia Jambor )

'It's not a personal attack, it's fact': Nationals candidate

Mr Oakeshott is also somewhat amused at the tag line for the campaign: "Tell Rob it's time to get a real job".

"Everyone should tell the National Party that representing the seat of Cowper is a real job," he said.

Former police officer and lawyer Patrick Conaghan is the National Party's candidate for Cowper — he said the line has nothing to do with becoming an MP.

He confirmed he saw the flyer before it went out, but said the National Party advertisements are a matter for the party.

"I don't agree that it's a personal attack on Rob, it's stating facts and not bullying," Mr Conaghan said.

"I've run a really clean campaign for the last six months.

"Rob and I have a healthy respect for each other."

Cowper has long been a National Party stronghold

The answer to why things have become so heated in Cowper can be found in the seat's history.

Cowper has been held by the Nationals and their predecessors for 117 of the 119 years that the seat has existed, and by the retiring MP Luke Hartsuyker since 2001.

At the 2016 election, Mr Oakeshott contested the seat and, despite starting his campaign three weeks from polling day, gained 26.3 per cent of the vote, outpolling Labor and reducing the National Party margin to just 4.5 per cent.

Mr Oakeshott's campaign in 2019 is expected to be boosted by the general swing against the government and the Nationals' loss of their retiring MP.