National's Simon Bridges asked if he trusts Judith Collins

National leader Simon Bridges has brushed off speculation of a leadership challenge from National MP Judith Collins.

"I'm confident in my leadership, I think I'm doing a good job, and I'm about to go into Caucus as I do every single Tuesday," Bridges told media as he headed into the weekly meeting.

When asked if he trusts Collins, Bridges refused to mention her by name, saying: "I trust my colleagues, and I'm not going to play these semantic silly games in the media."

Bridges said: "Look, I always talk about three things: holding the Government to account, developing our plans and what we do there, and the need for discipline and unity - and today's no different."

Newshub has been told the numbers are firming for Collins to take a leadership role - a position she has previously put her hand up for.

Earlier on Tuesday, Collins refused to say she's loyal to Bridges, telling Newshub: "I support the leader", when asked if she could say, 'I am loyal to Simon Bridges'.

"I am loyal to the National Party - the National Party of course is not a cult and I always support the leader and he was chosen as the leader just over a year ago so I absolutely support him," Collins said.

National MPs Newshub spoke to on Tuesday showed support for Bridges, with Amy Adams saying: "I think the majority of the Caucus is very clear that we support Simon."

National MP Maggie Barry told Newshub: "I support Simon Bridges as leader 100 percent."

MPs in Bridges' Caucus told Newshub earlier this month they are not pleased with their leader's handling of the Jami-Lee Ross saga, the "emotional junior staffer" issue, and 'slushy-gate', among others.

Bridges on Monday said Corrections spending $1 million on slushy machines for staff as "irresponsible and wasteful" - which a National MP described to Newshub as "petty".

A recent poll showed Bridges has dropped down to five percent as preferred Prime Minister, which is the lowest he had ever polled during his time as National leader - well-behind Prime Minister Jacinda Ardern on 51 percent.