|Up to 280,000 people in Sindh province have lost their homes this year due to rising flood waters [Reuters]
Floods triggered by monsoon rains have crippled Pakistan's biggest city and commercial hub of Karachi, with few people able to make it to work or school, government officials said.
Villages have been inundated by flood waters as canals have been breached and rain water has not adequately drained.
Many in the region are still recovering from last year's devastating floods, which brought widespread criticism of the government because of its slow response. About 800,000 families remain without permanent shelter, and more than one million people still need food assistance.
Pakistan's already unpopular government now faces another crisis as monsoon rains that have killed 200 people sweep through the southern Sindh province.
Al Jazeera's Kamal Hyder, reporting from Karachi, said: "Things are pretty desperate, as the heavy rains are pounding the entire city".
Hyder added that many Pakistanis have no no faith in their government to come to their rescue.
"The authorities are known to sleep at the time of urgency. These rains have been going on for several weeks now, which the government saw coming, but they've been caught napping, and any action is seen as too little too late," he said.
According to disaster management officials, new flood waters have made about 280,000 people homeless, destroyed or damaged 1.2 million houses and flooded 4.5 million acres since late August.
The United Nations offered to help the victims of the floods after the Pakistani government appealed for international assistance.
In Karachi, the capital of Sindh, rain was forecast through Wednesday or longer.
"We have recorded 50 to 100 [millimetres] of rain in Karachi and the situation is pretty bad. Many main roads and areas are inundated at the moment and it can turn even worse," said Mohammad Hussain Syed, the city's district co-ordination officer.
Officials at Pakistan's main stock market in Karachi were forced to close early on Tuesday due to negligible attendance and thin trade volumes, while many banks were also closed.
The state of Punjab is set to close all public and private educational institutions because of the threat of dengue fever caused by heaving flooding.
The 2010 floods killed about 2,000 people and made 11 million homeless in one of Pakistan's worst natural disasters.
One-fifth of Pakistan was then submerged in water, and the government faced a $10bn bill to repair damage to homes, bridges, roads and other infrastructure.
The Islamabad government will face another major setback if floods cause heavy damage to the vital agriculture sector.
Pakistan may also have lost up to two million cotton bales, or about 13 per cent of its estimated crop, due to heavy monsoon rains during harvesting in Sindh, government and industry officials said.
Aid workers expressed fears over possible outbreaks of diseases linked to the new floods, especially among children.
Karachi, on the Arabian Sea and the country's main port, contributes about two-thirds of the government's total tax revenue and 25 per cent of Pakistan's gross domestic product, according to officials.
Floods are the last thing the city of 18 million people needs as political, religious and sectarian violence, together with organised crime, has destabilised Karachi, prompting recent calls for a military crackdown.