The United Nations appealed for $357 million for flood-ravaged southern Pakistan.

An estimated 5.4 million people have been affected by the floods stemming from heavy monsoon rains. Nearly 1 million homes have been destroyed and 72 percent of crops lost in the worst affected areas in Sindh and Balochistan.

In launching its Rapid Response Plan on Sunday, the United Nations says it aims to provide food, water, sanitation, health and emergency shelter to those worst hit for six months.

The United Nations and its humanitarian partners have distributed more than 20,000 shelters and 530,000 plastic sheets and more than 650,000 people have received medicine and medical care.

The United Nations says it aims to provide access to safe drinking water for 400,000 people in the coming days and it expects 500,000 people will receive food aid by the end of the month.

"More than 5 million people are struggling to survive massive flooding across southern Pakistan and the rains continue to fall," Valerie Amos, undersecretary-general for the U.N. Office for the Coordination of Humanitarian Affairs, said in a statement.

"They have lost their homes, their possessions and their livelihoods. The next few days will be crucial, as the U.N. and partners help the government to get food, safe water and shelter to the most vulnerable. One year after the largest floods in recent history, the people of Pakistan are in desperate need again. We cannot let them down."

Pakistan's floods last year directly affected about 20 million people with a death toll of nearly 2,000. In that disaster, about one-fifth of Pakistan's total land area -- more than 307,000 square miles -- was underwater.

The amount of rainfall hitting the otherwise arid region this monsoon season was close to what it normally gets in five years, said Qamar-uz-Zaman Chaudhry, climate affairs adviser and vice president of the World Meteorological Organization, Asia Region.

"If we look at the frequency and the trend of the extreme weather events happening in Pakistan during the last two decades, it is easy to find its connection with climate change," Chaudhry told Pakistan's The News International.

In Sindh the rainfall is 270 percent and 1,170 percent above average for monsoon rains, respectively, for August and September, he said.

Chaudhry said that due to climate change, Pakistan could expect an increase in frequency and intensity of extreme weather events and more erratic monsoon rains, causing more frequent flooding and droughts.