The number covered just Khyber Pakhtunkhwa and Punjab as figures from southern Sindh province had not yet come in, National Disaster Management Authority chief Nadeem Ahmad told AFP in Islamabad.
Prime Minister Yousuf Raza Gilani appealed for immediate international help to cope with the disaster as authorities evacuated half a million people from risk areas in the south.
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"I would ask international community to support and help Pakistan alleviate sufferings of flood-affected people," Gilani said in a televised address to the nation.
"Pakistan has been hit by worst floods of its history," he said.
"The loss of human lives and infrastructure has been colossal and real assessment of damages can only be done when water recedes."
The nearly two-week-old disaster across the largely impoverished country hard hit by Taliban-linked violence washed away entire villages and killed at least 1600, according to UN estimates.
"We are passing through very critical times but courageous nations face such difficulties with strong will and determination," Gilani said, adding that floods were engulfing new areas even as he spoke.
Authorities in densely populated Sindh were busy evacuating villagers, warning that major floods in the next 48 hours threatened hundreds of communities in the fertile basin along the swollen Indus river.
"It is a real crisis all over the country. It is unprecedented floods in our history," military spokesman Major General Athar Abbas told AFP, adding that the country did not have the resources to cope with such a disaster.
Bedraggled women, children and elderly men in shabby clothes were deposited on the banks by rescue boats criss-crossing a giant lake dotted by tree tops in the village of Durrani Mehar in northern Sindh.
The meteorological office issued a red alert overnight, warning of an "imminent" and "extreme" flood threat to Sindh, especially along the Indus, as flooding spread to Indian-held Kashmir, where more than 110 people have now died.
Torrential rains were also forecast in the northwestern province of Khyber Pakhtunkhwa, where the disaster management authority warned people who have returned to partially damaged homes or those living along rivers to be careful.
The head of the flood relief operations in Khyber Pakhtunkhwa, Major General Ghayoor Mehmood, told reporters in Peshawar that the floods killed about 1400 people in the province, with 213 still missing.
"The scale of the needs is absolutely daunting," said Melissa Fleming, a spokeswoman for the office of the UN High Commissioner for Refugees.
More than 252,000 homes are thought to have been damaged or destroyed across Pakistan, and 558,000 hectares of crop land flooded, and it could take weeks before electricity is fully restored.
"Our cattle died and the cotton crop destroyed," said Mohammad Bakhsh, 50, a resident of Qasim Ghot village.
"I've got calls on my mobile saying 20 to 25 children from our family are stranded in the village and are holding onto tree branches.
"We are begging the authorities to rescue them. Two of my children have drowned and we don't know where they are," Bakhsh said.
The flooding has threatened electricity generation plants, forcing units to shut down in a country already suffering a crippling energy crisis.
Survivors have lashed out at authorities for failing to come to their rescue and provide better relief, piling pressure on a cash-strapped administration straining to contain Taliban violence and an economic crisis.
"We have nothing. I have no food and water to give my children. We desperately need help," Janat Bibi, a 30-year-old mother of eight, told AFP. Her husband Khadim Mirani was missing in the flood.
Particular scorn has been heaped on the unpopular President Asif Ali Zardari for pressing ahead with a visit to Europe at the height of the disaster.
Islamic charities, some with suspected links to extremist militants, have been stepping into the breach on the ground, as international relief efforts are mobilised, but aid workers are struggling to reach all those affected.
British charities grouped to launch an urgent appeal on TV and radio through the Disasters Emergency Committee, and France said it would give $US395,000 ($A431,270) to three organisations working to provide relief for the victims.
The United States has pledged a total of $US35 million ($A38.21 million) in aid, with military helicopter relief missions travelling into the worst-hit regions.
