The United Nations appealed on Tuesday for $160 million to help Pakistan as army helicopters rescued stranded families and dropped food packages into inaccessible areas following "epochal" rains and flooding.

The historic deluge, mainly triggered by abnormal monsoon rains, has killed more than 1,100 people, affected 33 million, and destroyed homes, businesses, infrastructure and crops.

"Pakistan is awash in suffering," U.N. Secretary-General Antonio Guterres said in a video message to launch the appeal in Islamabad and Geneva.

"The Pakistani people are facing a monsoon on steroids - the relentless impact of epochal levels of rain and flooding."

He said the scale of the country's needs - with millions forced from their homes and schools, health facilities and livelihoods destroyed by the climate catastrophe - required the world's collective and prioritised attention.

Nearly 300 stranded people, including some tourists, were airlifted in northern Pakistan, a state-run disaster management agency said in a statement, adding that over 50,000 people had been moved to two government shelters in the northwest.

People complained at the shelters.

"Life is very painful here," 63 year-old villager Sadiq Hussain told Reuters.

He said he and his family had to bear it all just because, "we lost everything."

Hussain said his entire village on the bank of Kabul river had escaped to safety. He was housed in the camps together with his parents and five children.

"Diarrhoea and fever is common here," he said of the camp, adding no sufficient medical assistance was available. He said he had already shifted his diabetic mother to a relative after she spent a harsh night at the camp.

"Life is bitter here," said Sidra Bibi who fled the same village as Hussain's.

Pakistan army chief General Qamar Javed Bajwa visited the northern valley of Swat and reviewed rescue and relief operations.

"We had no hope, but then army's help came," said one of the tourists in a video statement issued by the military. "Thank God we're rescued."

Bajwa told reporters that rescue and relief operations could be over, but that "the rehabilitation will take a long, long time."

'OBLIGATION TO HELP'

Early estimates put the damage from the floods at more than $10 billion, the government has said, adding that the world had an obligation to help Pakistan cope with the effects of man-made climate change.

Torrential rain has triggered flash floods that have crashed down from northern mountains, destroying buildings and bridges and washing away roads and crops.

Colossal volumes of water are pouring into the Indus river, which flows down the middle of the country from its northern peaks to southern plains, bringing flooding along its length.

Pakistan's foreign minister, Bilawal Bhutto-Zardari, said hundreds of thousands of women, children and men were living outdoors without access to food, clean water, shelter or basic healthcare.

"We urgently need shelter and tents, and mosquito nets," he said, adding that Pakistan would also need help with rehabilitation and reconstruction of the flood-hit areas.

Pakistan estimates the floods have affected more than 33 million people, or more than 15% of its 220 million population.

Guterres said the $160 million he hoped to raise with the appeal would provide 5.2 million people with food, water, sanitation, emergency education and health support.

General Akhtar Nawaz, chief of the national disaster agency, said at least 72 of Pakistan's 160 districts had been declared calamity-hit.

More than two million acres of agricultural land were flooded, he said.

'GROUND ZERO FOR GLOBAL WARMING'

Bhutto-Zardari said Pakistan had become ground zero for global warming.

"The situation is likely to deteriorate even further as heavy rains continue over areas already inundated by more than two months of storms and flooding," he said.

Guterres appealed for a speedy response to Pakistan's request to the international community for help, and called for an end to "sleepwalking towards the destruction of our planet by climate change."