Boris Johnson has told world leaders he is growing “increasingly frustrated” that their commitments to tackle the climate crisis are “nowhere near enough”.

The Prime Minister warned during a meeting at the United Nations in New York that the gap between what industrialised nations have promised and what they are actually delivering remains “vast”.

He urged them to redouble their efforts to hit a key financing pledge to help developing nations, which he has conceded there is only a “six out of 10” chance of hitting before the UK hosts the Cop26 climate summit in November.

But Joe Biden’s climate envoy, John Kerry, raised hopes that the target will be met, hinting that the US President could announce more money.

Co-hosting a discussion at the UN General Assembly, the Prime Minister noted that “everyone nods and we all agree that something must be done”.

“Yet I confess I’m increasingly frustrated that the ‘something’ to which many of you have committed is nowhere near enough,” he said.

“It is the biggest economies in the world that are causing the problem, while the smallest suffer the worst consequences.

“And while progress is being made all over the world, the gulf between what has been promised, what is actually being delivered, and what needs to happen… it remains vast.

“Too many major economies – some represented here today, some absent – are lagging too far behind.”

Mr Johnson issued a stark warning over what would happen if they do not redouble their efforts to hit the target of giving 100 billion dollars (£73 billion) a year in support to developing nations to cut their carbon emissions and protect themselves against environmental change.

“If you say that the lives of their children are not worth the hassle of reducing domestic coal consumption, will they vote with you in fora such as this?” he said.

“Will they work with you, borrow from you, stand with you if you tell the world that you don’t care whether their land and their people slip below the waves?

“To be merely a bystander is to be complicit in their fate – yet that is exactly what you will be if you fail to act this year.”

Mr Johnson has downplayed the chances of hitting the 100 billion dollar target before he hosts Cop26 in Glasgow.

But, in New York, Mr Kerry told Sky News: “I think we’re going to get it done by Cop and the US will do its part.”

Asked if Mr Biden will announce more funds this week, the adviser said: “I’m not hoping… I’m telling you to stay tuned into the president’s speech and we’ll see where we are.”

The Prime Minister said he would wait to see what Mr Biden had to say, and that an increased US commitment would make a “huge difference” but “we are not counting our chickens”.

“We have been here before, we have all heard lots of pledges, lots of positive noises, let’s see where we get to,” he told reporters in New York.

But a change in the US commitment would “send a massively powerful signal to the world”, Mr Johnson added.

He said the Cop26 summit in Glasgow could be a “turning point for the world” and “the moment when we have to grow up and take our responsibilities”.

Downing Street has said developed countries have “collectively failed” on their 100 billion dollar target, with OECD figures last week showing that only 79.6 billion dollars in climate finance was mobilised in 2019.

The Prime Minister will meet Amazon boss Jeff Bezos on Monday and has vowed to tell him the online giant must pay its fair share of taxes in the UK and address working standards for employees.

Mr Johnson is also expected to challenge Brazil’s president Jair Bolsonaro, a notorious climate change sceptic, on deforestation during a separate meeting.