Opposition leader Simon Bridges has accused the Prime Minister of hypocrisy on climate change, saying while she told the United Nations no one has the luxury of "copping out" she did just that when she met with United States President Donald Trump.

And Bridges has also continued to criticise the "Christchurch Call", despite dozens more countries now joining the effort to eliminate online terrorist content.

Ardern issued a plea during her keynote speech at a United Nations Climate Summit private sector forum in New York this morning, attended by heads of state and business leaders.

"No one has the luxury of copping out. Not those who deny climate change, nor those who believe it's too far gone," she said.

"Now is the time for optimism and for hope and, crucially, a plan."

Ardern also met Trump in New York but earlier this week indicated she had no plans to raise climate change with the president, who pulled the US out the Paris Agreement.

Afterwards the meeting, Ardern told reporters they discussed trade, tourism, Christchurch and the gun buyback and that she had briefly raised the Climate Summit itself.

Bridges on Tuesday said if he had the president's ear he would have talked about climate change.

"The Prime Minister has said around climate change … 'No one has the luxury of a cop-out on this.' And yet, when she met with the leader of the free world, that's exactly what she did," Bridges said.

"She copped out with the person who could make the most difference on climate change in the world."

The opposition leader also still wouldn't back down on his earlier criticism of the Christchurch Call but also criticised Ardern for not raising it with Trump either.

"Without the United States onboard, this is a toothless tiger," Bridges said.

"This is some nebulous, feel-good stuff that won't achieve anything."

It was announced on Tuesday that 31 new countries had joined the call - a global effort to tackle online extremism in the wake of the Christchurch mosque shootings - including Mexico, Sri Lanka and Chile, with the Council of Europe and UNESCO also adding their voices. That takes the total number of member countries to 48.

The US, however, is still holding out from signing, though it has been involved in the ongoing work.

The Call's work will be driven by a Global Internet Forum to Counter Terrorism (GIFCT) - set up by Facebook, Twitter, Google (YouTube) and Microsoft in 2017 - which will become an independent body tasked with preventing and responding to terrorist and violent extremism online.

It will have dedicated teams focused on a set of goals, potentially lead to radicalisation including looking at the companies' algorithms that potentially lead to radicalisation.