Heavy rain has been forecast for tomorrow as well, and schools and colleges have been told not to open.
The met department expects the rain to ease a little by about 11:30 pm. City officials will then pull an all-nighter if they are to clear roads and train tracks for tomorrow morning's rush hour.
Mumbai rains: People braved waist-deep water in many parts of the city.
"It isn't a panic situation but only step outside your house is absolutely necessary," tweeted Aditya Thackeray, whose Shiv Sena party controls the city's municipal corporation. By that time, television channels were showing people wading in knee-deep water and railway stations packed with people desperate to get home.
Fights were diverted, delayed and cancelled - for a brief period, the airport closed down altogether. The total breakdown of the city brought comparisons to 2005, when relentless rain wrecked the city.
"I haven't been able to travel and had to cancel all my plans," said researcher Rajesh Prabhakar, who was stranded on the outskirts of Mumbai after his train was cancelled. "Many of my friends are stranded at railway stations... this is a reminder of the 2005 floods."
Most commuters are struggling in knee-deep water
Cars were stranded; some people including film director Mahesh Bhatt spoke of being rescued from flooded cars. One driver lowered his window to show that he was nearly knee-deep in water inside his sedan. As the evening rush hour approached and there was no sign of the rain easing up, the Mumbai police urged people to abandon their cars if the water was tyre-high.
Rainwater flooded the King Edward Memorial Hospital in central Mumbai, forcing doctors to vacate the pediatric ward.
"We are worried about infections...the rain water is circulating rubbish that is now entering parts of the emergency ward," said Ashutosh Desai, a doctor in the 1,800 bed hospital.
Social media saw churches, gurudwaras and residents offering shelter to those stuck miles from home.