Mumbaikars witnessed severe water-logging on the streets after the city received heavy rainfall on Saturday.
In this regard, trains on Central Railways suburban are running with a delay of 10-12 minutes, though there is no cancellation at present.
The Indian Meteorological Department had declared the onset of monsoon over Maharashtra's Mumbai and Thane.
This was reflected in Mahim and Marine Drive areas of Mumbai, in addition to Thane.
Apart from Maharashtra, heavy rainfall was also witnessed in Karnataka's Mangaluru city and Madhya Pradesh's capital of Bhopal, bringing respite from soaring temperatures.
Earlier, the IMD had forecast that the monsoon would hit Maharashtra and surrounding areas by June 6, and rainfall could be expected by June 7.
Fearing crisis situation due to heavy rainfall, the Brihanmumbai Municipal Corporation (BMC) on cancelled the weekly Saturday and Sunday offs for its officers.
Monsoon has already hit Kerala, Tamil Nadu, Andhra Pradesh, and North-East, and will move up north from Maharashtra.