United Nations Secretary-General Antonio Guterres has warned the climate emergency "is a race we are losing" and called for countries to lift their commitments to cut emissions.

"This is not a climate talk summit. We have had enough talk," he said at a UN climate meeting on Monday.

"This is not a climate negotiation summit. You don't negotiate with nature. This is a climate action summit."

Nearly 70 countries - about two-fifths of those signed up to the Paris Agreement - have indicated they will increase climate action.

But Prime Minister Scott Morrison is holding fast to Australia's target of cutting emissions by 26-28 per cent from 2005 levels by 2030.

"I'm committed to what I took to the Australian people; that was 26 per cent for 2030 and that's what we'll achieve," he told reporters in Chicago, where he gave a foreign policy speech while the climate summit was opening in New York.

Foreign Minister Marise Payne represented Australia at the climate summit.

Asked if he felt the need to say something about longer-term targets in response to Mr Guterres, Mr Morrison said: "Not at this point."

Instead of stronger emissions targets, Mr Morrison is focused on practical environmental actions.

"It's about plastics, it's about oceans, it's about recycling," he said.

The prime minister also suggested China should now be treated as a developed - rather than developing - economy in addressing global environmental challenges.

"If the goal is to reduce emissions, then you obviously got to focus on the places which have the largest emissions," he said.

Australia's emissions have increased over the past few years, while the USA's have been trending downwards for a decade.

Meanwhile, youth climate activist Greta Thunberg lambasted world leaders in her address to the UN summit.

"You have stolen my dreams and my childhood with your empty words," she said.

"People are suffering. People are dying. Entire ecosystems are collapsing. We are at the beginning of a mass extinction - and all you can talk about is money and fairytales of eternal economic growth."

Opposition Leader Anthony Albanese criticised the prime minister's decision to skip the climate change summit.

Mr Albanese said with Australia's carbon emissions on the rise, it was not good enough to demand that other countries take action.

"It's about time the government put in place an energy and climate change policy," he told reporters in Bendigo.

Former prime minister Kevin Rudd said Mr Morrison "couldn't be bothered" to speak at the summit.

"This is a global challenge requiring global leadership and national leadership," he told the ABC.

"When you have a prime minister of the country not stepping up to the plate, addressing the world's forum, and indicating what Australia's future carbon reduction commitments will be, it sends a very clarion clear message ... that the Australian government is just not serious."

Australian Associated Press