Torrential overnight rains in Dhaka broke a half-century record, the met office said on Tuesday as the city, half-submerged by morning, ground to a halt.
Meteorlogists said 333mm of rain was recorded in the capital over the 24-hour period up to 7am, breaking a 53-year-old record in Dhaka for the month of July.
The unusually heavy rain occurred due to a conjunction of a monsoon front and a depression in the Bay of Bengal, Rasheduzzaman, of the Dhaka meteorological office, told bdnews24.com.
"The phenomenon is called a 'cloud outburst'," he said.
"This is the highest rainfall ever recorded in a 24-hour period in July in the capital. The average rainfall for the entire month is just 373mm in Dhaka," he said.
"Of the record 333mm, most of the rainfall occurred in just six hours between 1am and 7am, which recorded 290mm of rainfall alone," said Rasheduzzaman.
It marks the highest recorded rainfall for the month since July 13, 1956, when 326mm was recorded in Dhaka.
The highest recorded rainfall for any month in the capital for a 24-hour period was 341mm in September 2004.
The all-time high for a 24-hour period anywhere in the country was recorded in Chittagong, at 425mm on June 11, 2007.
The record rains came after weeks of dry weather during the peak monsoon months, bringing fears of drought for Aman farmers in the north.
Dhaka, with its collapsing amenities and creaky drainage, was keeping afloat with difficulty amid the severe flooding in the morning.
The Dhaka water authority deployed a total of 250 pumps the capital to alleviate the water logging crisis that left half the city knee-to-waist deep in floods.
Boats were seen plying the some of the worst-hit areas in the morning. Bashabo, Mugda, Meradia, Maghbazaar, Mouchak, Mohammadpur, Shantinagar, Mirpur, and parts of Old Dhaka faced the most severe water logging.
Major roads and junctions were unpassable for most of the night and through the morning, residents of vulnerable areas were seen pumping or bailing water out of their houses through the night and into the morning.
Rail services were also suspended in the morning and two international flights were unable to land at Zia International Airport, said officials.
Thousands of morning commuters were stranded without transport, while offices, schools and markets in low-lying areas were inundated.
The Bangladesh Secretariat office blocks were floating like islands in feet-deep water on Tuesday morning. Dhaka Stock Exchange was forced to delay start of trade by an hour as the floor was flooded and elevators out of order.
The rain had eased off by midmorning, but weathermen said the city was likely to see more rainfall through the day.
They said the coastal districts have also been asked to keep hoisted local cautionary signal three until further notice.
Local government minister Jahangir Kabir Nanak, speaking to reporters after an emergency meeting at WASA Bhaban in the morning, said, ""We sympathise with those who have been suffering immensely due to the unusually heavy rains. All WASA officials have been combating the water-logging across the city since early morning."