The India Meteorological Department (IMD) on Wednesday evening issued a red alert for Mumbai and its neighbouring districts, predicting "extremely heavy rainfall".
It has been raining in many parts of the city since afternoon.
A civic official said the IMD upgraded its orange alert for the country's financial capital to red alert, which is valid till 8.30 am on Thursday.
In its latest warning, issued at 5.30 pm, IMD has predicted "extremely heavy rainfall and thunderstorms with lightning and gusty winds at isolated places very likely" in Mumbai, Thane, Raigad and Ratnagiri districts.
The weather bureau has issued an orange alert for the coastal districts of Palghar and Sindhudurg with "heavy to very heavy rainfall and thunderstorms with lightning and gusty winds at isolated places very likely".
Mumbai's island city has been witnessing heavy rains since evening, while it has been pouring in many suburban pockets since afternoon.
Mulund and its surrounding areas experienced the heaviest rainfall, resulting in waterlogging in low-lying areas.
Heavy rains slowed down road traffic due to waterlogging and poor visibility. Suburban train services, considered the lifeline of Mumbai, were also delayed due to rains, said officials. -- PTI