United Nations chief Antonio Guterres visited several flood-hit areas of Pakistan on Saturday as he rounded off a two-day trip aimed at raising awareness of the disaster.
Record monsoon rains and melting glacier in northern mountains triggered floods that have killed nearly 1,400 people and swept away houses, roads, railway tracks, bridges, livestock and crops.
Huge areas of the country are under water and hundreds of thousands of people have been forced from their homes. The government says the lives of nearly 33 million have been disrupted and estimates the damage at $30 billion.
Both the government and Mr Guterres have blamed the flooding on climate change.
"Pakistan and other developing countries are paying a horrific price for the intransigence of big emitters that continue to bet on fossil fuels," Mr Guterres said on Twitter shortly before leaving the Pakistani capital to see some of the most flood-affected areas.
"From Islamabad, I am issuing a global appeal: Stop the madness. Invest in renewable energy now. End the war with nature."
The UN secretary general travelled to the southern province of Sindh before flying over some of the worst-affected areas en route to Balochistan, another badly hit province in western Pakistan.
"It is difficult not to feel deeply moved to hear such detailed descriptions of tragedy," Mr Guterres said after landing in Sindh, according to a video released by the office of Prime Minister Shehbaz Sharif.
"Pakistan needs massive financial support. This is not a matter of generosity, it is a matter of justice."
A video released by Information Minister Maryam Aurangzeb showed Mr Guterres seated next to Mr Sharif viewing flood-damaged areas from an aircraft window.
"Unimaginable," Mr Guterres said while surveying the damage.
Pakistan received 391 millimetres of rain in July and August — nearly 190 per cent more than the 30-year average. Sindh received 466 per cent more rain than the average.
The effect of the torrential rain has been twofold: destructive flash floods in rivers in the mountainous north, and a slow accumulation of water in the southern plains.
Thousands of temporary campsites have mushroomed on slivers of dry land in the south and west — often roads and railway tracks.
With people and livestock cramped together, the camps are ripe for outbreaks of disease, with many cases of mosquito-borne dengue reported, as well as scabies.
"If he comes and sees us, Allah will bless him," Rozina Solangi, a 30-year-old housewife from a flooded village near Sukkur in Sindh, told AFP on Friday.
"All the children, men and women are roasting in this scorching heat. We have nothing to eat, there is no roof on our heads. So he must do something for us poor."
Mr Guterres said the world needed to understand the impact of climate change on low-income countries.
"Humanity has been waging war on nature and nature strikes back," he said.
"Nature strikes back in Sindh, but it was not Sindh that has made the emissions of greenhouse gases that have accelerated climate change so dramatically," he said.
"There is a very unfair situation relative to the level of destruction."
— With reporting from Reuters and AFP