Pakistan's PM Yusuf Raza Gilani says 20 million people have been affected by the country's floods, a much higher estimate than the UN's 14 million.
He was addressing the nation during much muted celebrations of Pakistan's independence from the UK 63 years ago.
The United Nations has confirmed at least one case of cholera among the victims, in the Swat valley.
Health workers have been stepping up their battle against waterborne diseases in the flood-hit country.
In his address, Mr Gilani said 20 million were now homeless, although it was unclear how many of those people were briefly forced to leave their homes and how many had lost their houses altogether.
"Unfortunately, the recent unprecedented torrential rains and devastating floods have made more than 20m people homeless, destroyed standing crops and food... worth billions of dollars, washed away bridges, roads, communication and energy networks," he said.
There were still flood victims to be reached, but the government was leaving no stone unturned, he said.
The UN had previously said the region's worst flooding in 80 years had affected 14 million out of Pakistan's 180 million population and killed 1,600 people.
UN Secretary General Ban Ki-moon is expected to visit the country during the weekend.
'Slow' international response
Meanwhile, Pakistan's UN envoy has voiced renewed criticism of the international response to the disaster.
Zamir Akram told the BBC that the immensity of the devastation was only now being recognised, and that so far there had not been enough help.
However, he said he was hopeful that the relief effort was improving.
"I don't think that Pakistan has been abandoned. As the gravity of the situation and the extent of the damage that has been caused by these unprecedented floods spreads around the world, the response is growing," he said.
And flood levels are expected to surge even higher along parts of the already dangerously swollen Indus river, with disaster officials saying "major peaks" were expected next week in Punjab and Sindh provinces.
Aid agencies have been warning of the dangers of an outbreak of cholera since the onset of the floods.
The UN said it would start widespread treatment of the deadly disease.
Maurizio Giuliano, of the UN Office for Humanitarian Affairs, told AFP news agency that one case of cholera had now been confirmed in the town of Mingora, in the Swat valley
He said there were 36,000 more cases of people suffering from watery diarrhoea - one of the symptoms of cholera.
"Given that there are concerns about cholera, which is a very deadly disease, what we've started to do instead of testing them for cholera is to treat everyone for cholera," he said.
"We're not suggesting that everyone who has acute watery diarrhoea has cholera, but cholera is certainly a concern and that's why we're stepping up our efforts to treat cholera."
Pakistan has cancelled official celebrations of its Independence Day on Saturday, as officials try to co-ordinate relief efforts.
Earlier, President Asif Ali Zardari directed that there should be no official celebrations.
In his Independence Day message, he said: "The enthusiasm of Independence Day this year... has been dampened because of the unprecedented floods that have devastated the lives of thousands of people and left scars on the lives of several hundred thousands more in all parts of the country.
"I salute the courage and heroism of flood victims and assure them that the government will do everything possible to alleviate their sufferings."
Major cultural and music shows will be cancelled along with the usual military parades and official gatherings.
Mr Zardari will instead spend the day touring affected regions in Khyber Pakhtunkhwa and Punjab provinces.
His critics at home and abroad have rounded on him for not taking a more direct role, and choosing to visit Europe just as the disaster was unfolding.
The UN on Wednesday launched a $459m (£294m) appeal for emergency aid, but says billions will be needed in the long term.
Analysts say the cost of agricultural losses is still hard to quantify.
The Crops Protection Association put the loss of the cotton crop alone at $1.8bn, while agriculture officials said 17 million acres of farmland was under water.