At least 20 million people — far more than previously thought — have been made homeless as a result of devastating floods in Pakistan, the country's prime minister announced Saturday.

Prime Minister Yousuf Raza Gilani gave the new homeless figure during a televised address.

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Caption: Displaced Pakistani flood-affected families live at the roadside in Qadirpur, 120 kilometres from Sukkur, Pakistan. ((Shakil Adil/Associated Press))

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The news came as the first reports of cholera emerged. The CBC's Adrienne Arsenault, reporting from Pakistan's hard-hit Swat Valley, said health workers think there may be thousands of cases of cholera across the country, with water contaminated in many areas.

"Doctors … who are here are telling us, clinically, it looks and seems like cholera," she said.

"People are hungry and, in a weakened state, it doesn't take long for those sort of vulnerable people to succumb."

The need for critical aid — both short and long-term — is growing. The UN has issued an urgent appeal for $460 million US in immediate assistance, but says billions will eventually be needed to help Pakistan recover from its worst flood disaster in memory.

Canada has already announced $2 million in aid and will follow that up later Saturday with the announcement of $30 million more, CBC News has learned.

Unusually heavy monsoon rains began falling in late July, causing massive flooding not seen in generations. At least 1,500 people have been killed and hundreds of thousands of homes have been swept away by the water.

More than 700,000 hectares of farmland have been wiped out.

More flooding is likely as rain continued to drench parts of the country Saturday. The vital River Indus has swollen to the point that it is 25 kilometres wide at some points.

The CBC's Arsenault reported that aid agencies are in place and working hard to distribute food and temporary shelter. But she said there are still many areas they can't reach.

"There are communities that are completely marooned and have had no contact with first responders," she said.

"All along the Swat Valley there are 37 bridges that are gone. These people cannot get to the other side.

"So the question remains: How are they doing?"