Up to 500 people from a government-run relief camp in Thatta town, in the worst-affected province of Sindh, blocked the main road between Karachi city and Thatta for three hours, calling for the state to provide food and shelter.
Residents complained they had not received food in the past two days.
Meanwhile hospitals are struggling to cope with a rising number of patients who express growing frustration with medical care.
Doctors say that patients are suffering from several diseases including gastroenteritis, diarrhea, skin and eye infections, and stocks of medecines are running low.
In addition, the United Nations has warned of imminent waterborne diseases, including typhoid fever, shigellosis and hepatitis A and E, and vector-borne diseases like malaria and dengue fever.
The monsoon floods have affected an estimated 18 million people, ravaged around a fifth of Pakistan's territory and destroyed over 3.4 million hectares of crops.
World Food Programme director Josette Sheeran has warned that Pakistan faces a triple threat to food supplies – with seeds, crops and incomes hit.
While the international community has now donated almost 550 million euros for humanitarian aid, the UN stresses the importance of a long term commitment of the latter in favour of the rehabilitation and reconstruction of the country.
Prime Minister Yusuf Raza Gilani said an inflation target of 9.5 per cent for 2011 would now likely be in the range of 15-20 per cent.
“Inflation is likely to spike significantly in the face of short supply of food due to crops destruction,” he told his cabinet in televised remarks.
He said that GDP growth would also lower to 2.5 per cent from the predicted 4.5 per cent.
“This economy loss will translate into massive job losses and loss of incomes for thousands of families,” he said.
"The budget deficit before the flood crisis was estimated to reach 4.5 per cent of GDP. Now it is estimated to be as much as 6-7 per cent of the GDP," Gilani told the cabinet.
"The floods have inflicted damage to the economy which may by some estimates reach 43 billion dollars, while affecting 30 per cent of all agricultural land," he said.
One million people have been displaced over the past few days alone. Pakistan’s government has confirmed 1,645 people dead and 2,479 injured but officials warn that millions are at risk from food shortages and disease.
The head of the UN refugee agency’s office in Peshawar, Ahmad Warsama, said that shelter would be provided for 80,000 people who could still not have access to their villages after flooded roads and broken bridges cut them off.
In the meantime, Pakistani air strikes on militant hideouts in a north-western tribal area killed 55 on Tuesday, with reports of some civilian deaths.
Militants are said to have used civilians as human shields, though security officials say the number of civilian casualties is unknown.
Officials also say Pakistani jet fighters Tuesday targeted rebels preparing for imminent suicide attacks and destroyed their bases in the Khyber tribal district, which borders Afghanistan.