More than 75 leaders are expected to speak over two days in Baku, but the heads of many top polluting nations are giving the crunch UN climate talks in the Azerbaijan capital a miss.

The conference comes at the end of what scientists say is almost certainly the hottest year on record, with warming driven mainly by burning coal, oil and gas.

In his opening address as host, Azerbaijani President Ilham Aliyev said his country and other oil and gas producers were not to blame.

"Quote me that I said that this is a gift of God, and I want to repeat it today," Aliyev told delegates in a stadium near the Caspian Sea.

"Oil, gas, wind, sun, gold, silver, copper, all... are natural resources and countries should not be blamed for having them and should not be blamed for bringing these resources to the market, because the market needs them."

Hungarian Prime Minister Viktor Orban also defended fossil fuels and said industry should not suffer in the fight against climate change.

"We must continue advancing the green transition while also maintaining our use of natural gas, oil and nuclear energy," he said.

Alex Rafalowicz from the Fossil Fuel Non-Proliferation Treaty Initiative said countries were not at fault for having natural resources "but they are responsible for the threat they pose to humanity by extracting them from the ground".

- 'Hurtling towards catastrophe' -

Few leaders from G20 nations -- which account for nearly 80 percent of global emissions -- are expected in Baku with US President Joe Biden, China's Xi Jinping and Indian premier Narendra Modi among those absent.

But UK Prime Minister Keir Starmer, one of the higher profile leaders attending, vowed Britain would aim to cut its emissions 81 percent from 1990 levels by 2035.

The updated climate goals are intended to show British "leadership on the climate challenge," he said.

The impact of Donald Trump's election victory was still being digested in Baku, where Washington's delegation sought to reassure that US efforts on global warming would not end.

UN climate chief Simon Stiell sought to reassure the talks that recent "political events" would not derail global climate diplomacy.

"Our process is strong. It's robust, and it will endure."

The meeting's top priority is landing a hard-fought deal to boost funding for climate action in developing countries.

These nations -- from low-lying islands to fractured states at war -- are least responsible for climate change but most at risk from rising seas, calamitous disasters and economic shocks.

"The reality is that these extreme weather events that the world is facing daily suggests that humanity, and the planet, are hurtling towards catastrophe," said Mia Mottley, prime minister of Barbados.

Some are pushing for the existing pledge of $100 billion a year to be raised tenfold at COP29 to cover the future cost of shifting to clean energy and adapting to climate shocks.

Nations have haggled over this for years, with disagreements over how much should be paid, and who should pay it.

Adonia Ayebare, the Ugandan chair of a bloc that groups over 100 mostly developing countries and China, said they had already rejected a draft deal on the table at Baku.

- Appeal for help -

Developing countries warn that without adequate finance, they will struggle to offer ambitious updates to their climate goals, which countries are required to submit by early next year.

Leaders from climate-vulnerable countries including the Maldives warned: "We need the finance COP to deliver."

"We see funds flowing freely to wage war, but scrutinised when it's for climate adaptation," said Mohamed Muizzu, president of the archipelago.

Mottley said hundreds of billions of dollars could be raised for climate action by taxing fossil fuel extraction, aviation and shipping.

"We need to consider levies," she said.

The small group of developed countries that pay for climate finance want the donor pool expanded to include wealthy emerging economies like China and the Gulf states, something firmly rejected by Beijing.

UN Secretary General Antonio Guterres on Tuesday said developing nations "must not leave Baku empty-handed".

"A deal is a must," he said.