UN secretary general Antonio Guterres has labelled the floods in Pakistan “a climate catastrophe” as he called for global action to help the country.

In a video message to launch a major UN appeal to help victims, Mr Guterres said the Pakistani people are facing “a monsoon on steroids – the relentless impact of epochal levels of rain and flooding”.

And he urged the world to “stop sleepwalking” into the destruction of the planet due to rising temperatures – hitting out at countries for putting climate action on the back burner and the world in growing danger.

“This climate catastrophe has killed more than 1,000 people with many more injured,” he said.

Let’s stop sleepwalking towards the destruction of our planet by climate change. Today, it’s Pakistan. Tomorrow, it could be your country

“Millions are homeless, schools and health facilities have been destroyed, livelihoods are shattered, critical infrastructure wiped out, and people’s hopes and dreams have washed away.”

Mr Guterres said dealing with the crisis requires the world’s collective and prioritised attention, as he launched a 160 million US dollar (£137 million) appeal to help provide 5.2 million people with food, water, sanitation, emergency education, protection and health support.

South Asia is one of the world’s global climate crisis hotspots – an area where people are 15 times more likely to die from climate impacts – he warned.

“As we continue to see more and more extreme weather events around the world, it is outrageous that climate action is being put on the back burner as global emissions of greenhouse gases are still rising, putting all of us – everywhere – in growing danger,” he said.

“Let us work together to respond quickly and collaboratively to this colossal crisis.

“Let us all step up in solidarity and support the people of Pakistan in their hour of need.

“Let’s stop sleepwalking towards the destruction of our planet by climate change. Today, it’s Pakistan. Tomorrow, it could be your country.”

Boris Johnson said the UK would send a “fitting” package of support to Pakistan after the “heart-rending” situation caused by flooding.

Speaking to reporters in Dorset, and asked if the UK will be sending a package of aid to Pakistan following the devastating flooding, the Prime Minister said: “Yes of course, and I can tell you that our sympathies are very much with the people of Pakistan.”

He described the “devastation” in the country as “absolutely heart-rending”.

Mr Johnson added: “Pakistan is traditionally one of the biggest recipients of UK overseas aid and we will of course make sure that we send a fitting package commensurate with the vital relationship that there is between the UK and Pakistan and people’s natural sympathies with those who have been affected by the floods.”

Haroon Altaf, regional director for Asia at disaster relief charity ShelterBox, said the logistics of getting shelter aid to the people in greatest need present a complicated challenge, with little dry land and communities cut off.

It’s going to take time, money, a huge humanitarian effort, and international support to help people in Pakistan to fully recover

He said: “With so much attention on other crises, resources are fewer. They may not be sufficient and that’s deeply concerning given that the floods will get worse in some parts of Pakistan over the next few weeks.

“It’s going to take time, money, a huge humanitarian effort, and international support to help people in Pakistan to fully recover, which is why we’ll be assessing how ShelterBox can help those most severely affected.”

Green Party co-leader Carla Denyer said the floods in Pakistan were the reality of the climate crisis.

She said: “We’re all seeing the impact of this emergency more and more at home in the UK, but as climate scientists have warned, the most brutal impacts are being experienced by poorer countries who have actually contributed a lot less to global CO2 emissions.”

Ms Denyer called on richer countries to honour previous pledges to provide funding for the loss and damage poorer countries suffer from climate change and for much greater levels of finance, delivered as grants rather than loans.