Pakistan's commercial capital, Karachi, has been paralysed by floods as torrential rain continues to lash southern Sindh province.Schools have shut down, many markets were forced to close and commuters had to abandon their vehicles as rain water flooded the streets.Villages across the province have been inundated as canals have been breached and water has not adequately drained.Many in the region are still recovering from last year's devastating floods.Millions were displaced across the country and at least 1,600 people died as torrential monsoon rains in 2010 caused rivers to burst their banks, washing away homes and property. Sindh was one of the worst affected regions.Some officials have said this year's floods could prove to be as serious.After two weeks of heavy rain, almost one million houses in Sindh have been destroyed or damaged and floods have affected nearly 4.2m acres of land, the UN saysMore than 200,000 people are estimated to have been made homeless by the floods and are living in temporary shelters or out in the open. Stranded families need food and drinking water but can only be reached by boat or helicopter.The BBC's Aleem Maqbool in Thatta, and on the way to the badly-affected district of Badin, says that areas affected by last year's floods have not escaped the latest rains - although they seem to have escaped the worst so far.Thatta now hosts a camp for 100 families who escaped the deluge further inland. But, our correspondent says, the Thatta market street is under water.The United States has sent food and medical aid to Pakistan for the millions affected by flooding, which has now killed 226 people.Food aid for hundreds of thousands of Pakistanis has been despatched, a state department spokesperson told the AFP news agency. The US will also answer Pakistan's appeal for assistance by sending tents and other non-food items.China has already pledged $4.7m (£2.96) for urgent humanitarian assistanceOn Monday the UN said it had begun efforts to feed 500,000 people affected by the floods and rain, initially concentrating its efforts in the badly-hit Badindistrict of Sindh province.Pakistan's disaster management chief also warned that the situation is worsening each day as water levels are rising because of poor drainage.In Karachi, the capital of Sindh, many streets were flooded and impassable to vehicles."I thought I would be able to make it to work, but it was a wrong decision. Now I am stuck. My car has broken down and I can't even find anyone for help," banker Khalid Hussain told Reuters news agency.Many main roads have been inundated and the situation could become worse, the city's district co-ordinator told Reuters. Karachi's stock exchange was set to close early, but one report said it had reversed this planNeighbouring India has also been affected by heavy monsoon rain.The government in India's eastern Orissa state has intensified its efforts to deliver aid as more than one million people were displaced and at least 16 killed by floods in recent days.About 2,600 villages have been submerged across 19 districts and 11 people are missing.Officials there say the rains have eased somewhat but more is forecast for the coming days.From / BBC