National Party leader Judith Collins has ramped up her attempts to dent Labour leader Jacinda Ardern's credibility, saying Ardern had "lied" about Covid-19 and failed on so many promises nobody should believe her now.

Among her claims, Collins said Ardern "lied" about the Covid-19 testing of border workers and she hoped Ardern sued her for that statement: "happy to prove it."

Collins spent the day in the north of Wellington, stopping first at Grenada to announce National was re-committing to a link road between the suburbs of Grenada and Petone.

Collins then went to Waikanae, where the bowling club was full for her public meeting alongside Otaki candidate Tim Costley.

At both meetings, Collins urged party supporters not to vote strategically by splitting their votes, an apparent bid to stop votes going to Act.

"We are utterly serious about taking this election, and it can be done. It can be done if every single person goes out and party votes National. Do not waste your vote on minor parties, or on people who will already be there."

There was also plenty of Ardern-bagging for National supporters to feast on at both events.

In Waikanae, she claimed Ardern "lied" when she had said all staff working at the border or in managed isolation and quarantine facilities were being regularly tested for Covid-19.

"Who let Covid-19 in? I tell you who did. Jacinda Ardern and her government.

"She told us on June 23 everybody was being tested. What a lie. When she said she went hard and fast, she went slow and pathetic. And she lied to us about what was happening."

"She lied. Gee, I hope she sues me for it. Happy to prove it."

Ardern later dismissed Collins' statements as "opposition politics".

Collins was referring to a government directive on June 23 for all staff in border and managed isolation roles to be regularly tested.

However, after the second outbreak in August it was found that about 60 per cent of staff had not been tested at all, and the Government had to boost the process and make it compulsory.

The source of that second outbreak has not been identified.

Collins criticised Ardern for a lack of delivery on everything from Kiwibuild to "light-rail pipe dreams".

She repeated her claim that Ardern would end up adopting some form of 'wealth tax' despite Ardern's repeated rejections of it as the "last roll of the misinformation dice".

"They're coming after you," Collins told the audiences at both events.

Collins later defended continuing to make that claim.

"If Labour get the chance to form the Government, yes they will have the Greens there whether they need them or not. Why? So they can blame them for the unpopular policies they put in place."

Asked later if people should be able to trust the promises Ardern made, Collins said that was difficult based on a track record which included KiwiBuild, light rail, and fees-free for students.

"Almost everything she said she would deliver she has failed to deliver. So why would I suddenly now, suddenly, start believing anything she said on her promises?"

One of those in the audience at Waikanae was former Prime Minister Jim Bolger, who had a quick word with Collins but did not want to offer any advice. "[She's] doing very well."

Bolger's 1993 quip "bugger the polls" may be the advice she needed.