The United Nations has launched an appeal for $459 million US to provide immediate humanitarian assistance to millions of people affected by devastating floods in Pakistan.

The UN Office for the Co-ordination of Humanitarian Affairs said "the worst monsoon-related floods in living memory" have affected more than 14 million people, and left between six million and seven million people in need of urgent food aid, clean water and shelter.

UN humanitarian chief John Holmes told CBC News that it's too early to say what the reaction to the appeal will be, but he said the new resources are needed to help meet urgent needs.

"If we don't have those resources, that means that more people will die and more people will suffer," Holmes said.

"These are people who have lost everything," he said. "They've lost their village, their house, their assets, their crops — and in some cases, even members of their own family."

Canada has already pledged $2 million in humanitarian aid. International Co-operation Minister Bev Oda said Wednesday that Canada will respond in a "significant way" to the UN appeal.

"We make sure whatever we commit to do is going to be used, and directly help those people in need," Oda said.

"We work with those on the ground to see what can be done, to [see] how we can ensure our offers will be directly helping those that are victims."

Oda told CBC News that Canada "will step up to the plate" to help people in need of assistance.

NDP Leader Jack Layton said the government should send Canada’s disaster response team and more money for humanitarian aid. Canada's large Pakistani community is "crying out" for more help from the government, Layton said.

"We'd like to see aid commensurate with the magnitude of the crisis," Layton told reporters in Ottawa on Wednesday.

Logistical challenges limit relief efforts

UN agencies, relief organizations and government officials are working to deliver relief supplies to flood affected areas, but heavy rains and swollen rivers have created enormous logistical challenges.

Vehicles drive through a flooded road in Charsadda in Pakistan's northwest on Wednesday. (Mohammad Sajjad/Associated Press)

“The scale of the crisis is so big that there’s huge numbers of people that are beyond the reach of the state and the international community,” said Matthew Green, a Financial Times correspondent.

The World Food Program has delivered a one-month ration of food to over 370,000 people in recent days, and hopes to reach over two million more in the next 10 days.

"We're particularly concerned about the needs of 600,000 people in the north of Khyber Pakhtunkhwa province," WFP Pakistan director Wolfgang Herbinger said in a statement.

"These people can only be reached by helicopter and for three days over the weekend — because of the bad weather — our helicopters were not able to fly."

While waters are receding in parts of the hard-hit northern province of Khyber Pakhtunkhwa, flooding continues in Punjab and Sindh province, the UN said.

The waters have damaged or destroyed at least 288,000 homes, wiped out villages and devastated road and communication networks.

"More than one week after the initial arrival of the floods, hundreds of thousands of people remain without electricity, piped water and communications," the UN said in a report.

Long-term reconstruction costs are expected to be in the billions, officials have said.

Holmes launched the appeal Wednesday which will cover the immediate relief period of up to 90 days.

With files from The Associated Press