Prime Minister Malcolm Turnbull has shot down calls from Liberal Party backbenchers to make the big four banks exempt from his plan to reduce the company tax rate.

Coalition MPs have called for the big four banks to excised from a tax plan the government hopes will cut the top corporate tax rate from 30 to 25 per cent by 2026.

“The company tax rate has got to really go across all corporations,” Mr Turnbull told reporters in Queenstown, New Zealand, on Saturday.

“Distinguishing between one sector or another is not a practical measure, I’m not aware of that ever being done.”

Four days after Commonwealth Bank posted a record half-year profit of $2.9 billion, Mr Turnbull said he “can understand” concerns about the practices of major banks like Commonwealth, ANZ, NAB and Westpac.

“We’re taking real action to ensure the banks treat their customers better and we’re taking action now,” he said.

Mr Turnbull also responded to the Labor party’s calls for a royal commission into banking after former Labor premier Anna Bligh was announced as the next CEO of the Australian Bankers’ Association on Friday.

“I can understand and I empathise with the reason many people want to call for a royal commission but the problem with the royal commission is that it will not actually result in any action,” Mr Turnbull said.

“You would have years and years of very expensive inquiry and then you’d have a report with some recommendations. The recommendations would be, essentially, to do the things we’re doing now.”

Shorten wants royal commission

Labor leader Bill Shorten said the government has to stop running a “protection racket” for the big banks after the prime minister shot down a proposal to exempt the major four lenders from company tax cuts.

“On one hand Mr Turnbull doesn’t want to have a royal commission into banks and on the other hand he wants to give them billions of dollars in tax giveaways,” Mr Shorten said in Darwin on Saturday.

Mr Turnbull’s policy to “look after the very rich” won’t stimulate economic growth, he said.

“It’s been estimated by Goldman Sachs, Mr Turnbull’s old investment bank, that something like 60 per cent or $30 billion of this corporate tax cut will go straight overseas.

“Nothing less than a royal commission will satisfy me … Australians are sick and tired of financial scandals,” he said.

Turnbull says ‘no thanks’ to NZ refugee offer

During his time in New Zealand, Mr Turnbull also said a polite “no, thanks” to the NZ government’s offer to take 150 refugees from Australia’s offshore detention network.

NZ Prime Minister Bill English revealed the longstanding proposal remains on the table after his first formal catch-up with his counterpart.

“[The offer] is one that we appreciate but our focus is on completing the arrangements with the United States,” Mr Turnbull told reporters in Queenstown on Saturday before flying out of the country.

Mr Turnbull said the visit had been valuable in reaffirming the relationship across the Tasman.

Accompanied by their economic teams, the pair discussed their common interest in free trade during Friday’s formal talks, especially after the US’ withdrawal from the Trans-Pacific Partnership – and their economic challenges.

“I’m looking forward to seeing a lot more of Bill,” Mr Turnbull said.

“I’m looking forwards to getting him out on the water on a kayak.”

The invitation follows the paddle Mr Turnbull took Mr English’ predecessor John Key on during their so-called “pyjama diplomacy” catchup last February.

“I’m not excessively competitive when it comes to kayaking but I do notice that if he’s good enough to beat a champion shearer I suspect his upper body strength might be pretty awesome.”

– with AAP