Ottawa is offering an additional $31 million in aid to Pakistan, where an estimated 20 million people have been left homeless by devastating floods that are now moving into the south.

House Leader John Baird made the announcement Saturday in Toronto, at what was to be an official flag-raising ceremony commemorating Pakistan Independence Day outside Queens Park.

Ottawa had previously pledged $2 million in aid for Pakistan last month, bringing Canada's combined donation to a total of $33 million.

In Pakistan, the government canceled its celebrations marking the country's creation and independence from Britain in 1947.

Instead, President Asif Ali Zardari met with flood victims in the northwest of Pakistan, where a deadly case of cholera had just been confirmed.

Aid workers expect more cases of cholera as the water-borne disease makes its way through the region.

And the cholera discovery came as new flood surges hit the south, shoving millions more people out of their homes.

Fresh flood waves swelled the River Indus on Saturday, where parts of the river are more than more 25 kilometers -- 25 times wider than during normal monsoon seasons.

Authorities are trying to warn people of the rising waters in Jacobabad, Hyderabad, Thatta, Ghotki, Larkana and other areas.

According to the United Nations, the number of people affected ranks this disaster worse than the combined toll of the Indian Ocean tsunami in 2004, the Kashmir earthquake in 2005 and this year's earthquake in Haiti.

Michael O'Brien of the International Red Cross said the scope of devastation "is pretty difficult to get your mind around."

"I think the sooner we realize that these problems can only be solved with a major contribution from the international community, the faster we'll be able to mobilize the kind of relief that's required," O'Brien told CTV News Channel by telephone from Islamabad on Saturday.

Some of the numbers in this disaster, which began in late July with heavy monsoon rains:

• Hundreds of thousands of homes have been destroyed

• 20 million people are now homeless, though it's unclear how man are displaced temporarily

• An estimated 1.7 million acres (nearly 700,000 hectares) of farmland has been wiped out

• About 1,600 people have died, but the toll could rise as disease spreads

This week, UN officials said $460 million is needed for immediate relief, followed by billions more to rebuild once the floodwaters finally recede.

The international community's slow, relatively muted response to the flooding disaster has many speculating why more has not been done.

"The international recognition of this disaster has not yet been sufficient to its dimensions," U.S. envoy Richard Holbrooke told the Council on Foreign Relations. "That is because floods, unlike earthquakes and tsunamis, are not sudden catastrophes that hit and then the reconstruction begins. They're rolling crises, which grow and are initially underestimated."

Other theories being considered include donor fatigue or the colouring of international attitudes toward Pakistan by links to terrorism or corruption.

Some even suggest Pakistan's own handling of the disaster has done little to instill confidence foreign aid would be put to good use.

U.S. President Barack Obama congratulated Pakistan on its Independence Day and said the U.S. would not abandon the country in its time of need.

"We will remain committed to helping Pakistan and will work side by side with you and the international community toward a recovery that brings back the dynamic vitality of your nation," Obama said in a statement.

UN Secretary General Ban Ki-moon is expected to visit Pakistan soon, possibly over the weekend.

With files from The Canadian Press and The Associated Press